Method and apparatus for surgical navigation

ABSTRACT

A surgical navigation system for navigating a region of a patient that may include a non-invasive dynamic reference frame and/or fiducial marker, sensor tipped instruments, and isolator circuits. The dynamic reference frame may be placed on the patient in a precise location for guiding the instruments. The dynamic reference frames may be fixedly placed on the patient. Also the dynamic reference frames may be placed to allow generally natural movements of soft tissue relative to the dynamic reference frames. Also methods are provided to determine positions of the dynamic reference frames. Anatomical landmarks may be determined intra-operatively and without access to the anatomical structure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 10/941,782 filed on Sep. 15, 2004; which is acontinuation-in-part of U.S. patent application Ser. No. 10/688,068filed on Oct. 17, 2003 The disclosures of the above applications areincorporated herein by reference.

FIELD

The present invention relates generally to navigated surgery, and morespecifically, to systems and methods for using instruments and systemsto assist in navigating surgical procedures in internal body structures.

BACKGROUND

Image guided medical and surgical procedures utilize patient imagesobtained prior to or during a medical procedure to guide a physicianperforming the procedure. Recent advances in imaging technology,especially in imaging technologies that produce highly-detailed, two,three, and four dimensional images, such as computed tomography (CT),magnetic resonance imaging (MRI), fluoroscopic imaging (such as with aC-arm device), positron emission tomography (PET), and ultrasoundimaging (US) has increased the interest in image guided medicalprocedures.

Typical image guided navigation systems generally require dynamicreference frames to track the position of the patient should patientmovement occur during the assisted procedure. The dynamic referenceframe is generally affixed to the patient in a generally permanent orimmovable fashion. The dynamic reference frame may also be used as afiducial marker and may, therefore, be attached to the patient duringthe acquisition of pre-operative images. This enables the image space tobe aligned with patient space during the navigated procedure. Forexample, with relation to a cranial procedure, the dynamic referenceframe can be attached to the skull by a bone screw. For other proceduresthe dynamic reference frame may be fixed to other boney portions alsowith bone screws. Regardless, the dynamic reference frame may include aportion that is fixed to the patient during the acquisition of thepre-operative images and remains attached until the procedure iscomplete to insure proper and accurate correlation between image spaceand patient space. Requiring that the dynamic reference frame beattached to the patient during the time that the pre-acquired images areacquired until the procedure actually takes place may be uncomfortable.

The dynamic reference frame may, then be used to assure that images of apatient, such as pre-acquired or atlas images, may be registered to thepatient space. Generally this registration also allows for tracking ofvarious instruments during a procedure. The tracked instruments willgenerally include portions that may be tracked and super-imposed overacquired or modeled images of the patient.

Various instruments may be used during an operative procedure that aredesired to be tracked. Even if images are acquired, eitherintra-operatively or pre-operatively, the instrument is generallyillustrated, and superimposed on the captured image data to identify theposition of the instrument relative to the patient space. Therefore, theinstrument may include detectable portions, such as electromagneticcoils or optical detection points, such as LEDs or reflectors, that maybe detected by a suitable navigation system.

Size considerations generally make it difficult to position the trackingsensors near a portion of the instrument to be positioned within thepatient, such as the distal tip. Because of this, the tracking sensorsare generally positioned within the handle of the instrument. Therefore,complex calculations and a degree of error may exist to determine theexact position of a distal end of the instrument relative to theposition of the detectable sensors. Also the instruments may flexunexpectedly so that the known dimensions are no longer true dimensionsof the instrument. Therefore, it may be desirable to provide sensorssubstantially near the distal tip or end of an instrument positionedwithin a patient.

The tracking of various sensor portions, such as electromagnetic coils,may require the transmission of a current or a voltage to or from thesensors. Therefore, an electrical potential is provided to an instrumentthat is often positioned within a portion of the patient's anatomy,which may include various portions such as the cardiac area,neurological area, and other areas of the patient. In order to provideseparation of these potentials from the patient, it may also bedesirable to isolate the potentials from the patient.

SUMMARY

A surgical navigation system for navigating a region of a patientincludes a non-invasive dynamic reference frame and/or fiducial marker,sensor tipped instruments, and isolator circuits. The dynamic referenceframe may be repeatably placed on the patient in a non-invasive mannerand in a precise location for guiding the instruments. The instrumentsmay be precisely guided by positioning sensors near moveable portions ofthe instruments. The patient may be electrically isolated from varioussources of current during the procedure.

According to various embodiments a surgical navigation system includes amethod of forming an electromagnetic sensing coil in a medicalinstrument. The method may include forming a core of a conductivematerial and forming a coil about the core. The core is covered with afirst layer of a material and a second layer of a material may alsocover the core, and at least part of the first layer. The coil may besubstantially electrically isolated from the core.

According to various embodiment a surgical navigation system for asubstantially minimally invasive dynamic reference frame is disclosed.The dynamic reference frame may include a body portion selectivelyattachable to a portion of the anatomy. It may also include a navigationportion to at least one of sense and transmit a characteristic. Aholding section is able to hold the body portion relative to the portionof the anatomy. The holding section may substantially non-invasivelyholds the body portion relative to the portion of the anatomy.

According to various embodiments a surgical navigation system fornavigating a procedure relative to a patient having an electricalisolating portion. The navigation system may include an electricalsource and an instrument including a conducting element disposable nearthe patient. A transmission medium may interconnect the electricalsource and the instrument. An electrical isolator may electricallyisolate the instrument from the electrical source.

According to various embodiments, a navigation system for determiningthe location of a member relative to an anatomy may includes a trackingsystem and a sensor to be sensed by the tracking system. Ananti-rotation mechanism may be provided to interconnect the sensor withthe anatomy. The anti-rotation mechanism contacts at least two points onthe anatomy to resist rotation of the sensor relative to the anatomy.

According to various embodiments a navigation system for determining aposition of a sensor relative to a portion of an anatomy including softtissue may include a localizer operable to produce a field relative tothe anatomy and a tracking sensor for sensing the field producedrelative to the tracking sensor to determine a position of the trackingsensor in the field. A housing may include and/or house the sensor. Thehousing is operable to allow movement of the sensor relative to the softtissue when affixed to the anatomy subcutaneously.

According to various embodiments a method of navigating a procedurerelative to an anatomy with a tracking system including a localizer anda tracking sensor positioned relative to the anatomy includes providinga plurality of coils in the tracking sensor in a fixed geometry. Thetracking sensor may be positioned at a location relative to the anatomyand the position of each of the plurality of coils may be determined. Atleast one of the plurality of the coils positioned may be determinedbased at least in part on the determined sensed position of theplurality of coils. Wherein determining the position includesdetermining a geometry of each of the coils and comparing the determinedgeometry to the fixed geometry.

According to various embodiments a method of navigating a procedurerelative to an anatomy with a tracking system including a localizer anda tracking sensor positioned relative to the anatomy is disclosed. Themethod may include providing a plurality of coils in the tracking sensorand positioning the tracking sensor at a location relative to theanatomy. A position of each of the plurality of coils may be determinedand averaging each of the determined position of the plurality of coils.The position of the tracking sensor may be determined based at least inpart on the averaging of each of the determined positions.

According to various embodiments a method of navigating a procedurerelative to an anatomy with a tracking system including a localizer anda tracking sensor positioned relative to the anatomy may includeproviding a plurality of coils in the tracking sensor and positioningthe tracking sensor at a location relative to the anatomy. Dataregarding the position of the plurality of coils may be collected with aweight datum for each of the plurality of coils. A weight for the datacollected regarding each of the plurality of coils may be determinedalong with a position of each of the plurality of coils.

According to various embodiments a method of using a tracking system toassist in reduction of interference in relation to the tracking systemmay include forming a field with a mobile localizer. An interferencemember may be determined and the mobile localizer may be moved to reducethe affect of the interference member.

According to various embodiments a method of navigating an anatomicalposition of an anatomy with an ultra-sound system may includespositioning the ultra-sound system relative to a selected portion of theanatomy and determining a plurality of points relative to a firstportion of the anatomy subcutaneously. A first point may be selectedwithin the determined plurality of points relative to the first portionof the anatomy. Also, a plurality of points may be determined relativeto a second portion of the anatomy subcutaneously and a second point maybe selected within the determined plurality of points relative to thesecond portion of the anatomy. A relationship between the first pointand the second point may be determined.

According to various embodiments a system for navigating a tool mayinclude a tracking system. A tracking sensor operable to be tracked bythe tracking system may also be provided. An engagement member mayinterconnect the tracking sensor with a tool. The tracking system may beoperable to track the tool.

Further areas of applicability will become apparent from the detaileddescription provided hereinafter. It should be understood that thedetailed description and various examples, while indicating variousembodiments, are intended for purposes of illustration only and are notintended to limit the scope of the description or the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a diagram of a navigation system according to variousteachings of the present invention;

FIGS. 2A and 2B are diagrams representing undistorted and distortedviews from a fluoroscopic C-arm imaging device;

FIG. 3 is a top perspective view of a non-invasive dynamic referenceframe according to various embodiments;

FIG. 4 is a cross-sectional view of the non-invasive dynamic referenceframe of FIG. 3;

FIG. 5 is an environmental application of the non-invasive dynamicreference frame of FIG. 3;

FIG. 6 is a sensor bobbin that may be used in the non-invasive dynamicreference frame of FIG. 3;

FIG. 7 is an environmental view of another non-invasive dynamicreference frame according to various embodiments;

FIG. 8 is an environmental view of another non-invasive dynamicreference frame according to various embodiments

FIG. 9 is an exploded perspective view of another non-invasive dynamicreference frame according to various embodiments;

FIG. 10A is a side elevational view of a stylet;

FIG. 10B is a detail interior view of a connection portion of the styletof FIG. 10A;

FIG. 11 is a cross-sectional view of a probe including a navigationsensor;

FIG. 12 is an enlarged view of the probe about circle 12 in FIG. 11;

FIG. 13 is a cross-sectional view of a suction instrument according tovarious embodiments;

FIG. 14 is an enlarged view about the circle 14 of FIG. 13;

FIG. 15 is a view of a tip of the stylet of FIG. 9A;

FIG. 16 is a cross-sectional view of the stylet tip of FIG. 15 fromcircle 16;

FIG. 17 is a method of forming an electromagnetic sensor according tovarious embodiments;

FIG. 18 is a schematic view of an isolator circuit according to variousembodiments;

FIG. 19 is a detailed partial cross-sectional view of a portion of thepatient including a recessed DRF;

FIG. 20 is a perspective view of a DRF including an anti-rotationalmechanism according to various embodiments;

FIG. 21 is an exploded perspective view of a DRF including ananti-rotational mechanism according to various embodiments;

FIG. 21A is an elevational environmental detail view of the DRF of FIG.21;

FIG. 22 is an exploded perspective view of a DRF including ananti-rotation mechanism according to various embodiments;

FIG. 23 is a perspective view of a DRF including an anti-rotationmechanism according to various embodiments;

FIG. 24 is a DRF including an anti-rotation mechanism according tovarious embodiments;

FIG. 25A is a perspective view of an instrument including a trackingsensor according to various embodiments;

FIG. 25B is a perspective view of an instrument including a trackingsensor according to various embodiments;

FIG. 26 is an environmental view of the instrument including a trackingsensor of FIG. 25A in use;

FIG. 27A is a perspective view of a DRF according to variousembodiments;

FIG. 27B is a perspective view of a DRF according to variousembodiments;

FIG. 28A-C is an exemplary use of a DRF according to variousembodiments;

FIG. 28D is a detail environmental view of a use of the DRF of FIG. 27;

FIG. 29 is a detail perspective view of a mobile localizer;

FIG. 30 is an environmental view of the mobile localizer of FIG. 29 inuse;

FIGS. 31-33 are flow charts illustrating methods of determining aposition of a sensor according to various embodiments,

FIG. 34A is a detail partial cross-sectional view of a portion ofanatomy including a scanning element;

FIG. 34B is a detail from circle in FIG. 34A;

FIG. 35 is an environmental view of implants with tracking sensorsaccording to various embodiments;

FIG. 36 is a plan view of an instrument with a tracking sensorsaccording to various embodiments;

FIG. 37 is a detail plan view of an instrument including a trackingsensor on a stylet according to various embodiments;

FIG. 38 is a plan view of an instrument including a tracking sensor on astylet according to various embodiments;

FIG. 39 is an exploded view of a guide with a tracking sensor accordingto various embodiments;

FIG. 40 is a detail cross-sectional view of the guide of FIG. 39according to various embodiments;

FIG. 41 is an exploded view of a tracking sensor assembly according tovarious embodiments;

FIG. 42 is an exploded view of a tracking sensor assembly according tovarious embodiments; and

FIG. 43 is an exploded view of a tracking sensor assembly according tovarious embodiments.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

The following description of various embodiments is merely exemplary innature and is in no way intended to limit the invention, itsapplication, or uses. As indicated above, the present invention isdirected at providing improved, non-line-of-site image-guided navigationof an instrument, such as a stylet, probe, suction tube, catheter,balloon catheter, implant, lead, stent, needle, guide wire, insertand/or capsule, that may be used for physiological monitoring,delivering a medical therapy, or guiding the delivery of a medicaldevice, orthopedic implant, or soft tissue implant in an internal bodyspace to any region of the body.

FIG. 1 is a diagram illustrating an overview of an image-guidednavigation system 10 for use in non-line-of-site navigating of aninstrument. It should further be noted that the navigation system 10 maybe used to navigate any type of instrument, implant or delivery system,including guide wires, needles, drug delivery systems, cell deliverysystems, gene delivery systems, biopsy systems, arthroscopic systems,etc. Moreover, these instruments may be used to navigate or map anyregions of the body.

The navigation system 10 may include an optional imaging device 12 thatis used to acquire pre-, intra-, or post-operative or real-time imagesof a patient 14. The optional imaging device 12 is, for example, afluoroscopic x-ray imaging device that may include a C-arm 16 having anx-ray source 18, an x-ray receiving section 20, an optional calibrationand tracking target 22 and optional radiation sensors 24. Thecalibration and tracking target 22 includes calibration markers 26 (seeFIGS. 2A-2B), further discussed herein. A C-arm, or optional imagingdevice controller 28 captures the x-ray images received at the receivingsection 20 and stores the images for later use. The C-arm controller 28may also be separate from the C-arm 16 and/or control the rotation ofthe C-arm 16. For example, the C-arm 16 may move in the direction ofarrow 30 or rotates about a longitudinal axis 14 a of the patient 14,allowing anterior or lateral views of the patient 14 to be imaged. Eachof these movements involve rotation about a mechanical axis 32 of theC-arm 16. In this example, the longitudinal axis 14 a of the patient 14is substantially in line with the mechanical axis 32 of the C-arm 16.This enables the C-arm 16 to be rotated relative to the patient 14,allowing images of the patient 14 to be taken from multiple directionsor about multiple planes. An example of a fluoroscopic C-arm x-ray thatmay be used as the optional imaging device 12 is the “Series 9600 MobileDigital Imaging System,” from OEC Medical Systems, Inc., of Salt LakeCity, Utah. Other exemplary fluoroscopes include bi-plane fluoroscopicsystems, ceiling fluoroscopic systems, cath-lab fluoroscopic systems,fixed C-arm fluoroscopic systems, isocentric C-arm fluoroscopic systems,3D fluoroscopic systems, etc.

In operation, the imaging device 12 generates x-rays from the x-raysource 18 that propagate through the patient 14 and calibration and/ortracking target 22, into the x-ray receiving section 20. The receivingsection 20 generates an image representing the intensities of thereceived x-rays. Typically, the receiving section 20 includes an imageintensifier that first converts the x-rays to visible light and a chargecoupled device (CCD) video camera that converts the visible light intodigital images. Receiving section 20 may also be a digital device thatconverts x-rays directly to digital images, thus potentially avoidingdistortion introduced by first converting to visible light. With thistype of digital C-arm, which is generally a flat panel device, theoptional calibration and/or tracking target 22 and the calibrationprocess discussed below may be eliminated. Also, the calibration processmay be eliminated or not used at all for cardiac therapies.Alternatively, the imaging device 12 may only take a single image withthe calibration and tracking target 22 in place. Thereafter, thecalibration and tracking target 22 may be removed from the line-of-sightof the imaging device 12.

Two dimensional fluoroscopic images that may be taken by the optionalimaging device 12 are captured and stored in the C-arm controller 28.Multiple two-dimensional images taken by the imaging device 12 may alsobe captured and assembled to provide a larger view or image of a wholeregion of a patient, as opposed to being directed to only a portion of aregion of the patient. For example, multiple image data of a patient'sleg may be appended together to provide a full view or complete set ofimage data of the leg that can be later used to follow contrast agent,such as Bolus tracking.

These images are then forwarded from the C-arm controller 28 to anavigation computer controller or work station 34 having a display 36and a user interface 38. It will also be understood that the images arenot necessarily first retained in the controller 28, but may also bedirectly transmitted to the navigation computer 34. The work station 34provides facilities for displaying on the display 36, saving, digitallymanipulating, or printing a hard copy of the received images. The userinterface 38, which may be a keyboard, mouse, touch pen, touch screen orother suitable device, allows a physician or user to provide inputs tocontrol the imaging device 12, via the C-arm controller 28, or adjustthe display settings of the display 36. The work station 34 may alsodirect the C-arm controller 28 to adjust the rotational axis 32 of theC-arm 16 to obtain various two-dimensional images along different planesin order to generate representative two-dimensional andthree-dimensional images.

When the x-ray source 18 generates the x-rays that propagate to thex-ray receiving section 20, the radiation sensors 24 sense the presenceof radiation, which is forwarded to the C-arm controller 28, to identifywhether or not the imaging device 12 is actively imaging. Thisinformation is also transmitted to a coil array controller 48, furtherdiscussed herein. Alternatively, a person or physician may manuallyindicate when the imaging device 12 is actively imaging or this functioncan be built into the x-ray source 18, x-ray receiving section 20, orthe control computer 28.

The optional imaging device 12, such as the fluoroscopic C-arm 16, thatdo not include a digital receiving section 20 generally require theoptional calibration and/or tracking target 22. This is because the rawimages generated by the receiving section 20 tend to suffer fromundesirable distortion caused by a number of factors, including inherentimage distortion in the image intensifier and external electromagneticfields. An empty undistorted or ideal image and an empty distorted imageare shown in FIGS. 2A and 2B, respectively. The checkerboard shape,shown in FIG. 2A, represents the ideal image 40 of the checkerboardarranged calibration markers 26. The image taken by the receivingsection 20, however, can suffer from distortion, as illustrated by thedistorted calibration marker image 42, shown in FIG. 2B.

Intrinsic calibration, which is the process of correcting imagedistortion in a received image and establishing the projectivetransformation for that image, involves placing the calibration markers26 in the path of the x-ray, where the calibration markers 26 are opaqueor semi-opaque to the x-rays. The calibration markers 26 are rigidlyarranged in pre-determined patterns in one or more planes in the path ofthe x-rays and are visible in the recorded images. Because the truerelative position of the calibration markers 26 in the recorded imagesare known, the C-arm controller 28 or the work station or computer 34 isable to calculate an amount of distortion at each pixel in the image(where a pixel is a single point in the image). Accordingly, thecomputer or work station 34 can digitally compensate for the distortionin the image and generate a distortion-free or at least a distortionimproved image 40 (see FIG. 2A). A more detailed explanation ofexemplary methods for performing intrinsic calibration are described inthe references: B. Schuele, et al., “Correction of Image IntensifierDistortion for Three-Dimensional Reconstruction,” presented at SPIEMedical Imaging, San Diego, Calif., 1995; G. Champleboux, et al.,“Accurate Calibration of Cameras and Range Imaging Sensors: the NPBSMethod,” Proceedings of the IEEE International Conference on Roboticsand Automation, Nice, France, May, 1992; and U.S. Pat. No. 6,118,845,entitled “System And Methods For The Reduction And Elimination Of ImageArtifacts In The Calibration Of X-Ray Imagers,” issued Sep. 12, 2000,the contents of which are each hereby incorporated by reference.

While the optional imaging device 12 is shown in FIG. 1, any otheralternative 2D, 3D or 4D imaging modality may also be used. For example,any 2D, 3D or 4D imaging device, such as isocentric fluoroscopy,bi-plane fluoroscopy, ultrasound, computed tomography (CT), multi-slicecomputed tomography (MSCT), magnetic resonance imaging (MRI), highfrequency ultrasound (HIFU), positron emission tomography (PET), opticalcoherence tomography (OCT), intra-vascular ultrasound (IVUS),ultrasound, intra-operative CT or MRI may also be used to acquire 2D, 3Dor 4D pre- or post-operative and/or real-time images or image data ofthe patient 14. The images may also be obtained and displayed in two,three or four dimensions. In more advanced forms, four-dimensionalsurface rendering regions of the body may also be achieved byincorporating patient data or other data from an atlas or anatomicalmodel map or from pre-operative image data captured by MRI, CT, orechocardiography modalities. A more detailed discussion on opticalcoherence tomography (OCT), is set forth in U.S. Pat. No. 5,740,808,issued Apr. 21, 1998, entitled “Systems And Methods For GuildingDiagnostic Or Therapeutic Devices In Interior Tissue Regions” which ishereby incorporated by reference.

Image datasets from hybrid modalities, such as positron emissiontomography (PET) combined with CT, or single photon emission computertomography (SPECT) combined with CT, could also provide functional imagedata superimposed onto anatomical data to be used to confidently reachtarget sights within the patient 14. It should further be noted that theoptional imaging device 12, as shown in FIG. 1, provides a virtualbi-plane image using a single-head C-arm fluoroscope as the optionalimaging device 12 by simply rotating the C-arm 16 about at least twoplanes, which could be orthogonal planes to generate two-dimensionalimages that can be converted to three-dimensional volumetric images. Byacquiring images in more than one plane, an icon representing thelocation of a catheter, stylet, suction-probe, or other instrument,introduced and advanced in the patient 14, may be superimposed in morethan one view on display 36 allowing simulated bi-plane or evenmulti-plane views, including two and three-dimensional views.

These types of imaging modalities may provide certain distinct benefitsfor their use. For example, magnetic resonance imaging (MRI) isgenerally performed pre-operatively using a non-ionizing field. Thistype of imaging provides very good tissue visualization inthree-dimensional form and also provides anatomy and functionalinformation from the imaging. MRI imaging data is generally registeredand compensated for motion correction using dynamic reference frames(DRF) discussed further herein.

Positron emission tomography (PET) imaging is generally a pre-operativeimaging procedure that exposes the patient to some level of radiation toprovide a 3D image. PET imaging provides functional information and alsogenerally requires registration and motion correction using dynamicreference frames.

Computed tomography (CT) imaging is also generally a pre-operativetechnique that exposes the patient to a limited level of radiation. CTimaging, however, is a very fast imaging procedure. A multi-slice CTsystem provides 3D images having good resolution and anatomyinformation. Again, CT imaging is generally registered and needs toaccount for motion correction, via dynamic reference frames.

Fluoroscopy imaging is generally an intra-operative imaging procedurethat exposes the patient to certain amounts of radiation to provideeither two-dimensional or rotational three-dimensional images.Fluoroscopic images generally provide good resolution and anatomyinformation. Fluoroscopic images can be either manually or automaticallyregistered and also need to account for motion correction using dynamicreference frames.

Ultrasound imaging is also generally intra-operative procedure using anon-ionizing field to provide either 2D, 3D, or 4D imaging, includinganatomy and blood flow information. Ultrasound imaging providesautomatic registration and does not need to account for any motioncorrection.

With continuing reference to FIG. 1, the navigation system 10 furtherincludes an electromagnetic navigation or tracking system 44 thatincludes a localizer, such as a transmitter coil array 46, the coilarray controller 48, a navigation probe interface 50, an electromagneticinstrument, such as a stylet or catheter 52 and a dynamic referenceframe 54. It will be understood that the localizer may be anyappropriate localizer, such as an optical, an acoustic, or otherlocalizer depending upon the system for which the localizer is chosen.Further included in the navigation system 10 is an isolator circuit orbox 55. The isolator circuit or box 55 may be included in a transmissionline or interrupt a line carrying a signal or a voltage to thenavigation probe interface 50. Alternatively, the isolator circuitincluded in the isolator box 55 may be included in the navigation probeinterface 50, the instrument 52, the dynamic reference frame 54, thetransmission lines coupling the devices, or any other appropriatelocation. As discussed herein, the isolator box 55 is operable toisolate any of the instruments or patient coincidence instruments orportions that are in contact with the patient should an undesirableelectrical surge or voltage take place, further discussed herein.

It should further be noted that the entire tracking system 44 or partsof the tracking system 44 may be incorporated into the imaging device12, including the work station 34 and radiation sensors 24.Incorporating the tracking system 44 may provide an integrated imagingand tracking system. Any combination of these components may also beincorporated into the imaging system 12, which again can include afluoroscopic C-arm imaging device or any other appropriate imagingdevice.

The transmitter coil array 46 is shown attached to the receiving section20 of the C-arm 16. It should be noted, however, that the transmittercoil array 46 may also be positioned at any other location as well. Forexample, the transmitter coil array 46 may be positioned at the x-raysource 18, within or atop the OR table 56 positioned below the patient14, on siderails associated with the table 56, or positioned on thepatient 14 in proximity to the region being navigated, such as on thepatient's chest. The transmitter coil array 46 may also be positioned inthe items being navigated, further discussed herein. The transmittercoil array 46 includes a plurality of coils that are each operable togenerate distinct electromagnetic fields into the navigation region ofthe patient 14, which is sometimes referred to as patient space.Representative electromagnetic systems are set forth in U.S. Pat. No.5,913,820, entitled “Position Location System,” issued Jun. 22, 1999 andU.S. Pat. No. 5,592,939, entitled “Method and System for Navigating aCatheter Probe,” issued Jan. 14, 1997, each of which are herebyincorporated by reference.

The transmitter coil array 46 is controlled or driven by the coil arraycontroller 48. The coil array controller 48 drives each coil in thetransmitter coil array 46 in a time division multiplex or a frequencydivision multiplex manner. In this regard, each coil may be drivenseparately at a distinct time or all of the coils may be drivensimultaneously with each being driven by a different frequency. Upondriving the coils in the transmitter coil array 46 with the coil arraycontroller 48, electromagnetic fields are generated within the patient14 in the area where the medical procedure is being performed, which isagain sometimes referred to as patient space. The electromagnetic fieldsgenerated in the patient space induce currents in sensors 58 positionedin the instrument 52, such as the catheter, further discussed herein.These induced signals from the instrument 52 are delivered to thenavigation probe interface 50 through the isolation circuit 55 andsubsequently forwarded to the coil array controller 48. The navigationprobe interface 50 may provide all the necessary electrical isolationfor the navigation system 10. Alternatively, the electrical isolationmay also be provided in the isolator box 55. Nevertheless, as mentionedhere, the isolator assembly 55 may be included in the navigation probeinterface 50 or may be integrated into the instrument 52, and any otherappropriate location. The navigation probe interface 50 also includesamplifiers, filters and buffers required to directly interface with thesensors 58 in the instrument 52. Alternatively, the instrument 52 mayemploy a wireless communications channel as opposed to being coupleddirectly to the navigation probe interface 50.

The instrument 52, as will be described in detail below, is equippedwith at least one, and generally multiple, localization sensors 58. Theinstrument 52 can be a steerable catheter that includes a handle at aproximal end and the multiple location sensors 58 fixed to the catheterbody and spaced axially from one another along the distal segment of thecatheter 52. The catheter 52, as shown in FIG. 1 includes fourlocalization sensors 58. The localization sensors 58 are generallyformed as electromagnetic receiver coils, such that the electromagneticfield generated by the transmitter coil array 46 induces current in theelectromagnetic receiver coils or sensors 58. The catheter 52 may alsobe equipped with one or more sensors, which are operable to sensevarious physiological signals. For example, the catheter 52 may beprovided with electrodes for sensing myopotentials or action potentials.An absolute pressure sensor may also be included, as well as otherelectrode sensors. The catheter 52 may also be provided with an openlumen, further discussed herein, to allow the delivery of a medicaldevice or pharmaceutical/cell/gene agents. For example, the catheter 52may be used as a guide catheter for deploying a medical lead, such as acardiac lead for use in cardiac pacing and/or defibrillation or tissueablation. The open lumen may alternatively be used to locally deliverpharmaceutical agents, cell, or genetic therapies.

In an alternate embodiment, the electromagnetic sources or generatorsmay be located within the instrument 52 and one or more receiver coilsmay be provided externally to the patient 14 forming a receiver coilarray similar to the transmitter coil array 46. In this regard, thesensor coils 58 would generate electromagnetic fields, which would bereceived by the receiving coils in the receiving coil array similar tothe transmitter coil array 46. Other types of localization sensors orsystems may also be used, which may include an emitter, which emitsenergy, such as light, sound, or electromagnetic radiation, and areceiver that detects the energy at a position away from the emitter.This change in energy, from the emitter to the receiver, is used todetermine the location of the receiver relative to the emitter. Othertypes of tracking systems include optical, acoustic, electrical field,RF and accelerometers. Accelerometers enable both dynamic sensing due tomotion and static sensing due to gravity. An additional representativealternative localization and tracking system is set forth in U.S. Pat.No. 5,983,126, entitled “Catheter Location System and Method,” issuedNov. 9, 1999, which is hereby incorporated by reference. Alternatively,the localization system may be a hybrid system that includes componentsfrom various systems.

The dynamic reference frame 54 of the electromagnetic tracking system 44is also coupled to the navigation probe interface 50 to forward theinformation to the coil array controller 48. The dynamic reference frame54, briefly and discussed in detail according to various embodimentsherein, is a small magnetic field detector that is designed to be fixedto the patient 14 adjacent to the region being navigated so that anymovement of the patient 14 is detected as relative motion between thetransmitter coil array 46 and the dynamic reference frame 54. Thisrelative motion is forwarded to the coil array controller 48, whichupdates registration correlation and maintains accurate navigation,further discussed herein. The dynamic reference frame 54 can beconfigured as a pair of orthogonally oriented coils, each having thesame center or may be configured in any other non-coaxial or co-axialcoil configuration. The dynamic reference frame 54 may be affixedexternally to the patient 14, adjacent to the region of navigation, suchas on the patient's chest, as shown in FIG. 1. The dynamic referenceframe 54 can be affixed to the patient's skin, by way of a selectedadhesive patch and/or a tensioning system. The dynamic reference frame54 may also be removably attachable to fiducial markers 60 alsopositioned on the patient's body and further discussed herein.

Alternatively, the dynamic reference frame 54 may be internallyattached, for example, to the wall of the patient's heart or other softtissue using a temporary lead that is attached directly to the heart.This provides increased accuracy since this lead may track the regionalmotion of the heart. Gating may also increase the navigational accuracyof the system 10. Gating procedures may be particular important whenperforming procedures relative to portions of the anatomy that move on aregular basis, such as the heart or the lungs or diaphragm. Although, itis not necessary to provide gating, it may be selected to do so duringvarious procedures. Various gating procedures and techniques aredescribed, such as U.S. patent application Ser. No. 10/619,216 entitledNavigation “System For Cardiac Therapies” filed on Jul. 14, 2003, andincorporated herein by reference. Dynamic reference frame 54 accordingto various embodiments and a fiducial marker 60, are set forth in U.S.Pat. No. 6,381,485, entitled “Registration of Human Anatomy Integratedfor Electromagnetic Localization,” issued Apr. 30, 2002, which is herebyincorporated by reference.

It should further be noted that multiple dynamic reference frames 54 mayalso be employed. For example, an external dynamic reference frame 54may be attached to the chest of the patient 14, as well as to the backof the patient 14. Since certain regions of the body may move more thanothers due to motions of the heart or the respiratory system, eachdynamic reference frame 54 may be appropriately weighted to increaseaccuracy even further. In this regard, the dynamic reference frame 54attached to the back may be weighted higher than the dynamic referenceframe 54 attached to the chest, since the dynamic reference frame 54attached to the back is relatively static in motion.

The navigation system 10 may optionally further include a gating device62 such as an ECG or electrocardiogram, which is attached to the patient14, via skin electrodes 64, and in communication with the coil arraycontroller 48. Respiration and cardiac motion can cause movement ofcardiac structures relative to the instrument 52, even when theinstrument 52 has not been moved. Therefore, localization data may beacquired on a time-gated basis triggered by a physiological signal. Forexample, the ECG or EGM signal may be acquired from the skin electrodes64 or from a sensing electrode included on the instrument 52 or from aseparate reference probe. A characteristic of this signal, such as anR-wave peak or P-wave peak associated with ventricular or atrialdepolarization, respectively, may be used as a triggering event for thecoil array controller 48 to drive the coils in the transmitter coilarray 46. This triggering event may also be used to gate or triggerimage acquisition during the imaging phase with the imaging device 12.By time-gating or event gating at a point in a cycle the image dataand/or the navigation data, the icon of the location of the catheter 52relative to the heart at the same point in the cardiac cycle may bedisplayed on the display 36, such as disclosed in U.S. patentapplication Ser. No. 10/619,216, entitled “Navigation System For CardiacTherapies” filed on Jul. 14, 2003.

Additionally or alternatively, a sensor regarding respiration may beused to trigger data collection at the same point in the respirationcycle. Additional external sensors can also be coupled to the navigationsystem 10. These could include a capnographic sensor that monitorsexhaled CO₂ concentration. From this, the end expiration point can beeasily determined. The respiration, both ventriculated and spontaneouscauses an undesirable elevation or reduction (respectively) in thebaseline pressure signal. By measuring systolic and diastolic pressuresat the end expiration point, the coupling of respiration noise isminimized. As an alternative to the CO₂ sensor, an airway pressuresensor can be used to determine end expiration.

Briefly, the navigation system 10 operates as follows. The navigationsystem 10 creates a translation map between all points in theradiological image generated from the imaging device 12 and thecorresponding points in the patient's anatomy in patient space. Afterthis map is established, whenever a tracked instrument, such as thecatheter 52 or a pointing device 66 is used, the work station 34 incombination with the coil array controller 48 and the C-arm controller28 uses the translation map to identify the corresponding point on thepre-acquired image or atlas model, which is displayed on display 36.This identification is known as navigation or localization. An iconrepresenting the localized point or instruments are shown on the display36 within several two-dimensional image planes, as well as on three andfour dimensional images and models.

To enable navigation, the navigation system 10 must be able to detectboth the position of the patient's anatomy and the position of thecatheter 52 or other surgical instrument. Knowing the location of thesetwo items allows the navigation system 10 to compute and display theposition of the catheter 52 in relation to the patient 14. The trackingsystem 44 is employed to track the catheter 52 and the anatomysimultaneously.

The tracking system 44 essentially works by positioning the transmittercoil array 46 adjacent to the patient space to generate a low-energymagnetic field generally referred to as a navigation field. Becauseevery point in the navigation field or patient space is associated witha unique field strength, the electromagnetic tracking system 44 candetermine the position of the catheter 52 by measuring the fieldstrength at the sensor 58 location. The dynamic reference frame 54 isfixed to the patient 14 to identify the location of the patient in thenavigation field. The electromagnetic tracking system 44 continuouslyrecomputes the relative position of the dynamic reference frame 54 andthe catheter 52 during localization and relates this spatial informationto patient registration data to enable image guidance of the catheter 52within the patient 14.

Patient registration is the process of determining how to correlate theposition of the instrument or catheter 52 on the patient 14 to theposition on the diagnostic or pre-acquired images. To register thepatient 14, the physician or user may use point registration byselecting and storing particular points from the pre-acquired images andthen touching the corresponding points on the patient's anatomy with thepointer probe 66. The navigation system 10 analyzes the relationshipbetween the two sets of points that are selected and computes a match,which correlates every point in the image data with its correspondingpoint on the patient's anatomy or the patient space. The points that areselected to perform registration are the fiducial markers or landmarks60, such as anatomical landmarks. Again, the landmarks or fiducialpoints 60 are identifiable on the images and identifiable and accessibleon the patient 14. The landmarks 60 can be artificial landmarks 60 thatare positioned on the patient 14 or anatomical landmarks that can beeasily identified in the image data. The artificial landmarks, such asthe fiducial markers 60, can also form part of the dynamic referenceframe 54.

The system 10 may also perform registration using anatomic surfaceinformation or path information as is known in the art. The system 10may also perform 2D to 3D registration by utilizing the acquired 2Dimages to register 3D volume images by use of contour algorithms, pointalgorithms or density comparison algorithms, as is known in the art. Anexemplary 2D to 3D registration procedure, as set forth in U.S. Ser. No.60/465,615, entitled “Method and Apparatus for Performing 2D to 3DRegistration” filed on Apr. 25, 2003, which is hereby incorporated byreference. The registration process may also be synched to an anatomicalfunction, for example, by the use of the ECG device 62.

In order to maintain registration accuracy, the navigation system 10continuously tracks the position of the patient 14 during registrationand navigation. This is because the patient 14, dynamic reference frame54, and transmitter coil array 46 may all move during the procedure,even when this movement is not desired. Therefore, if the navigationsystem 10 did not track the position of the patient 14 or area of theanatomy, any patient movement after image acquisition would result ininaccurate navigation within that image. The dynamic reference frame 54allows the electromagnetic tracking device 44 to register and track theanatomy. Because the dynamic reference frame 54 is rigidly fixed to thepatient 14, any movement of the anatomy or the transmitter coil array 46is detected as the relative motion between the transmitter coil array 46and the dynamic reference frame 54. This relative motion is communicatedto the coil array controller 48, via the navigation probe interface 50,which updates the registration correlation to thereby maintain accuratenavigation.

The navigation system 10 can be used according to any appropriate methodor system. For example, pre-acquired images or atlas or 3D models may beregistered relative to the patient and patient space. Variousregistration regimens and techniques include those described in U.S.patent application Ser. No. 10/619,216 entitled “Navigation System ForCardiac Therapies” filed on Jul. 14, 2003. Generally, the registrationsystem allows the images on the display 36 to be registered andaccurately display the real time location of the various instruments,such as the instrument 52, and other appropriate items, such as thepointer 66. In addition, the pointer 66 may be used to register thepatient space to the pre-acquired images or the atlas or 3D models. Inaddition, the dynamic reference frame 54 may be used to ensure that anyplanned or unplanned movement of the patient or the receiver array 46 isdetermined and used to correct the image on the display 36.

As discussed above, the dynamic reference frame 54 may include anyappropriate dynamic reference frame, such as the selectively fixabledynamic reference frame 70 illustrated in FIG. 3. The dynamic referenceframe 70 generally includes a superior side 72 and an inferior side 74.

With continuing reference to FIG. 3 and additional reference to FIG. 4,the dynamic reference frame 70 includes a recess 76 as a portion of theinferior side 74. The recess 76 may be provided for any appropriatepurpose, such as receiving a selective adhesive. In addition, asdiscussed herein, the recess may be used to allow the gathering of softtissue relative to the dynamic reference frame 70. As described, thedynamic reference frame 70 may be affixed to the patient 14 in anyappropriate position.

An adhesive positioned in the adhesive recess 76 generally allows thedynamic reference frame 70 to be fixed to the selected point on thepatient 14. As discussed further herein, a tensioning apparatus may alsobe provided on the dynamic reference frame 70 to further assist holdingthe dynamic reference frame in a selected position. Further, the dynamicreference frame 70 defines a bore 78 to removably receive a selectedsensor or coil. As described herein, the sensor may be fitted into thesensor bore 78 and removed from the sensor bore 78 as selected. Forexample, should the dynamic reference frame 70 also be used as afiducial marker 60 it may be radio-or image-opaque, and the sensorbobbin 90 may be removed from the bore 78 during imaging of the patient14, such as acquiring MRI images. This eliminates any distortion thatmay be caused by the bobbin 90. Nevertheless, the sensor bobbin 90 mayalso be permanently provided within the sensor bore 78 for ease of useof the apparatus. It may be desirable to provide the dynamic referenceframe 70 as a substantially disposable exterior portion and the sensormay be reusable. In either case, the dynamic reference frame 70 may beformed of a plastic or other non-conductive material.

If the dynamic reference frame 70 is used as a fiducial marker, thedynamic reference frame 70 may define a localization divot 80. The divotor recess 80 allows the pointer 66 or any appropriate mechanism todetermine the location of the dynamic reference frame 70 relative to thepatient 14 or the patient space. Generally, the pointer 66 is able toengage the divot 80 in a selected manner in patient space, such that thenavigation system 44 is able to determine the position of the dynamicreference frame 70 relative to the patient 14. The pointer 66 is alsoengaged or used to point out the divot 80 in the pre-acquired image toregister the image space with the patient space. Therefore, detectedmovement of the dynamic reference frame 70 may be used to determinemovement of the patient 14. It will be understood that the divot 80 maybe positioned in any appropriate portion of the dynamic reference frame70 but is generally provided in an easily accessible and viewable area.moreover, there may be multiple divots 80 or landmarks, as discussedherein. The multiple divots 80 may be used as fiducial markers. Theredynamic reference frame 70 may also include a radio-opaque material tobe imaged in various imaging techniques.

With further reference to FIG. 3, the dynamic reference frame 70 mayinclude a concave recess 82 defined as a portion of the superior part 72of the dynamic reference frame 70. The recess 82 may be provided for anyappropriate purpose such as engaging a tensioning member 84. Thetensioning member 84 may include an adhesive strip that is appliedrelative to the dynamic reference frame 70 to ensure a substantialselected fixation of the dynamic reference frame 70 relative to thepatient 14.

With reference to FIG. 5, an exemplary use of the dynamic referenceframe 70 is illustrated. The dynamic reference frame 70 is affixed tothe patient 14 using an adhesive that is included in the adhesive recess76. In addition, the tensioning strip 84 is placed atop the recess 82 tofurther hold the dynamic reference frame 70. The tensioning strip 84helps by tensioning the dermis 86 of the patient 84 relative to thedynamic reference frame 70. Generally, the dermis 86 will form pucker ortension lines 88 to illustrate or ensure that the dynamic referenceframe 70 is substantially fixed to the patient 14. In this way, the softtissue to which the dynamic reference frame 70 is fixed and is not ableto move relative to the dynamic reference frame 70, thereby providing arelatively stable and secure attachment to the patient 14.

Although it is illustrated that the dynamic reference frame 70 may betensioned relative to the skin of the pectoral region of the patient thedynamic reference frame 70 may be tensioned relative to any appropriateportion of the anatomy. For example, the dynamic reference frame 70 maybe fixed relative to a posterior portion of the patient 14 relative tothe spine, if a spinal procedure is occurring. In addition, the dynamicreference frame 70 may be tensioned to the dermis on the forehead of thepatient, if a procedure relative to the cranium is being performed.Nevertheless, the dynamic reference frame 70 may be fixed to the dermiswith substantial force using the tensioning device 84.

Although the tensioning device 84 is illustrated to be a separate stripof material having an adhesive, it will be understood that thetensioning device 84 may be integrated into the dynamic reference frame70. For example, a tensioning system may be fixed to the superiorportion 72 of the dynamic reference frame 70 and a backing released toexpose an adhesive region to allow the tensioning system to tension thedermis relative to the dynamic reference frame 70. In addition,tensioning strips, that form the tensioning device 84 may be affixed toor formed integrally with any appropriate portion of the dynamicreference frame 70 to allow for easy use during an operative procedure.For example, tape or a belt may be used that may be separate or integralwith the dynamic reference frame 70. Therefore, it will be understoodthat the tensioning device 84 need not be limited according to anyselected embodiments and is provided to allow for tensioning the dermisrelative to the dynamic reference frame 70.

As is generally known by one skilled in the art, the dermis of anindividual is generally not substantially taught over the sub-dermalanatomy. That is, a portion of the anatomy may move relative to thedermis without the dermis moving. Although this may be desired forgeneral anatomical or natural movements, it may be desired to know theprecise movements of any portions of the anatomy of the patient 14during an operative procedure where the navigation system 44 is beingused.

The instrument 52, such as the catheter, may be engaged to a subdermalregion of the patient 14. Movement of any subdermal portion may beselected to be known during the operative procedure. In addition, theposition of the instrument 52 relative to the subdermal anatomicalportions may be selected to be substantially known. Therefore, thedynamic reference frame 70 may be fixed to the patient 14 to allow forensuring that the image on the display 36 substantially correctlyillustrates the position of the anatomy of the patient 14. If subdermalportions are allowed to move without the dynamic reference frame 70moving, however, it may be possible that the display 36 may notcorrectly display the proper location of the instrument 52 relative tothe subdermal anatomy of the patient 14. Therefore, the tensioning strip84 may allow for more closely tracking the movement of subdermalportions or portions of the anatomy of the patient 14 without using moreinvasive techniques.

Generally, the dynamic reference frame 70 may be affixed to the dermisor external portions of the patient 14. This allows the dynamicreference frame 70 to be fixed to the patient and used to reference theposition of the patient 14 relative to the position of the otherelements, such as the instrument 52 and the pointer 66, and to alsoensure the appropriate registration of the images on the display 36 in asubstantially non-invasive manner. Simply the dynamic reference frame 70need not penetrate the dermis to be fixed to a rigid portion of theanatomy, such as a bone portion. Therefore, the dynamic reference frame70 can be easily fixed and removed from the patient 14 as selected.

An electromagnetic bobbin or multiple coil member 90 may be positionedin the recess 78 of the dynamic reference frame 70. The sensor bobbin 90includes a body 92 that is generally formed from material that is notconductive to allow the coils to operate and sense a position in afield. In addition, the body 92 may be manipulated by a handle ormanipulable portion 94 extending from the body 92. In addition, thehandle 94 may allow leads or contacts from an external source, such asillustrated in FIG. 1, to be interconnected to the body portion 92 intothe coils 96 and 98.

The first coil 96 and the second coil 98 are generally positioned atangles relative to one another. These angles may be any appropriateangle such as a generally orthogonal angle or other appropriate angle.The two coils 96, 98 being positioned at angles relative to one another,allow for six degrees of freedom sensing including translation, angle,pitch, yaw, and rotation. Therefore, the position or movement of thedynamic reference frame 70 can be determined by sensing theelectromagnetic field of the coil array 46 with the first coil 96 andthe second coil 98

Generally, the body 92 of the bobbin 90 and the exterior or the bodiesof the dynamic reference frame 70 are formed of an appropriate material.For example, the material may be a non-metallic and non-conductingmaterial such as an appropriate ceramic, plastic, and the like. Thematerial may be selected from a material that will not interfere witheither transmitting or receiving information regarding the magneticfield and not interfere with imaging of the patient 14. Therefore, thematerial is a substantially non-conducting material, but may also bevisible in the image data.

In addition, the dynamic reference frame 70 may be used to address whatmay be referred to as skin shift. As described above the skin may moverelative to the subdermal anatomic portions. Therefore, the dynamicreference frame 70 may be fixed to the patient 14 in a manner tosubstantially eliminate error that may be introduced by a skin shift. Inaddition to the tensioning device 84, the tensioning device may be anyappropriate portion. For example, the tensioning device 84 may be a bandwhich substantially extends around the selected anatomical portion ofthe patient. For example, the dynamic reference frame 70 may be fixed toa band that substantially extends around the chest of a patient during aselected procedure. In addition, the dynamic reference frame 70 may beincluded on or integral with a band that substantially extends aroundthe cranium, the arm, the thigh, or any other appropriate member. Inaddition, the band may be substantially elastic to engage the selectedanatomical portion. The elastic band may be provided to substantiallytension the tissue relative to the dynamic reference frame, but notsimply in a localized tensioning manner. The dynamic reference frame 70can, therefore, be fixed to any appropriate portion of the body eitherwith the localized tensioning member 84 or a non-localized tensioningmember. The band may form a general tensioning while a tape portion mayform a more localized tensioning. The tensioning members allow fortensioning the dermal tissue over the subdermal anatomy to substantiallyeliminate skin movement relative to the subdermal area.

In addition, the dynamic reference frame 54 may be substantiallynon-invasively placed near a substantially rigid portion of the anatomy.For example, the dynamic reference frame may include a rhinal dynamicreference frame 100, as illustrated in FIG. 7. The rhinal dynamicreference frame 100 may include a body 102 and an optional tensioningdevice 104. The rhinal dynamic reference frame 100 is formed togenerally fit over a bridge 106 of a nose 108 of the patient 14.Generally, the bridge 106 of the nose 108 is covered with asubstantially thin layer of dermal tissue. Therefore, the bridge of thenose 106 is substantially rigid relative to the patient 14. In addition,the tensioning member 104 may be provided to stabilize any portion ofthe skin that may move relative to the bridge 106 of the nose 108.However, the adhesive portion fixed on the bottom of the dynamicreference frame 100 may simply be the only adhesive necessary to fix therhinal dynamic reference frame 100 to the bridge 106 of the nose.Nevertheless, the rhinal dynamic reference frame 100 may allow for thedynamic reference 100 to be fixed to the patient 14 in a substantiallyrigid and repeatable place.

Not only may the rhinal dynamic reference frame 100 be fixed to thebridge 106 of the nose, but the dynamic reference 100 may besubstantially molded to a particular portion of the nose 108. Therefore,a molded or moldable inferior portion 110 of the rhinal dynamicreference frame 100 may be fitted to a selected portion of the nose 108.The dynamic reference frame 100 may be positioned and repositionedrelative to the bridge 106 of the nose 108 a plurality of times withsubstantially repeatable placements of the dynamic reference frame 100.

The repeatable substantially precise placement enables the dynamicreference frame 100 to be removed and replaced onto the bridge 106 ofthe nose 108 without substantially introducing error into thepositioning of the dynamic reference frame 100. This allows initialpre-operative images to be taken with the dynamic reference frame 100 inplace and used as a fiducial marker. The rhinal dynamic reference frame100 may then be removed from the patient 14 prior to the operativeprocedure. Subsequently, during the operative procedure, the rhinaldynamic reference frame 100 may be repositioned on the patient 14.Because the molded portion 110 of the rhinal dynamic reference frame 100is substantially fitted to a particular portion of the bridge 106 of thenose 108, the rhinal dynamic reference frame 100 can be substantiallypositioned in the same position as during the pre-operative images.Therefore, the rhinal dynamic reference frame 100 allows forsubstantially error free referencing of the patient and registration ofthe patient 14 to the pre-operative images that may be displayed on thedisplay 36. This allows the rhinal dynamic reference frame 100 to beused as both the dynamic reference frame 54 and as a fiducial marker forregistering of the pre-operative images.

In addition, it will be understood that the dynamic reference frame 100may be positioned in any appropriate manner. As illustrated above, thedynamic reference frame 70 may be fixed to a substantially flat portionof the anatomy of the patient 14. Alternatively, the anatomic or rhinaldynamic reference frame 100 may be molded to a substantially uniquelyshaped portion of the anatomy of the patient 14. It will be understoodthat other portions of the anatomy may also be substantially molded tofit a particular portion of the anatomy.

With reference to FIG. 8, a further alternative embodiment of thedynamic reference frame includes an anatomic or inner-cochlear dynamicreference frame 111. The inner cochlear dynamic reference frame 111 isgenerally molded to fit a portion or the cochlear portion of the ear112. The cochlear portion of the ear 112 generally includes asubstantially unique topography that may be used to fit the dynamicreference frame 111 in substantially only one position. Therefore, asdiscussed in relationship to the rhinal dynamic reference frame 100 thatincludes the moldable portion, the inner-cochlear dynamic referenceframe 111 may also be formed, at least partially, of a moldablematerial.

For example, a distal portion 111 a of the inter cochlear implant 111may be formed of a substantially moldable material that may be press fitinto the cochlear portion 112 of the ear of the patient 14. After beingmolded to the cochlear portion 112 of the ear of the patient 14, themoldable material may be cured to substantially maintain the moldedshape. An exterior or proximal portion 111B of the inner-cochlearimplant 111, may be formed of a moldable or a non-moldable material.Therefore, the inner-cochlear implant 111 may be formed of twomaterials. Nevertheless the proximal portion 111 b, or any appropriateportion, may also include a first sensing coil 113 and a second sensingcoil 114. The sensing coils 113, 114 may be positioned in anyappropriate manner but may be positioned at angles relative to oneanother. Therefore, the inner-cochlear implant may provide six degreesof freedom information regarding motion of the inner-cochlear dynamicreference frame 111 during use.

The position of the sensors 113, 114 may be referenced and calibratedafter molding of the inner-cochlear implant 111. Therefore, the positionof the head of the patient 14 may be known based upon the sensedposition of the inner-cochlear dynamic reference frame 111. In addition,as discussed in relation to the other dynamic reference frames, thecoils 113, 114 may be passive or active. If the coils 113, 114 areactive, the inner-cochlear dynamic reference frame 111 may include apower source, such as battery.

The inner-cochlear dynamic reference frame 111 may also be substantiallymolded as a separate procedure. For example, such as forming aninner-cochlear hearing aid, the inner-cochlear dynamic reference 111 maybe molded to the cochlear portion of the ear of the patient 14 and theinner-cochlear dynamic reference frame 111 may be formed separatelyafter the impression is made. Nevertheless, the molding of theinner-cochlear dynamic reference frame 111 relative to the cochlearportion of the ear 112 with the patient 14, allows for a substantiallyrepeatable placement of the inner-cochlear dynamic reference frame 111relative to the patient 14. Therefore, images displayed on the display36 may be substantially easily registered relative to the known locationand repeatable location of the inner-cochlear dynamic reference frame111.

It will be understood that the molded portions may be substantiallypermanently molded or reusably molded. For example, a curable materialmay be included, in any appropriate dynamic reference frame, such as theinner-cochlear dynamic reference frame 111. The moldable portion of thecochlear implant 111 may be molded to a portion of the ear or press fitinto the ear and then cured to substantially maintain the molded shape.Therefore, the dynamic reference frames may be substantiallynon-invasively positioned relative to the patient to allow for dynamicreferencing of the patient 14 during the operative procedure.

In addition, the dynamic reference frame may be formed almost entirelyof the substantially molded material. Therefore, the dynamic referenceframe may include a molding material that may be molded to a selectedportion of the anatomy and then cured to maintain the shape of theanatomy and also may be formed to include an area to receive the sensorbobbin 90. Although it will be understood that any appropriate coils maybe used to form the sensor and may include substantially separate coilsthat can be positioned into the moldable material substantiallyseparately and removably.

It will also be understood that the dynamic reference frame 54 may befixed to any appropriate portion of the anatomy. As discussed above, thedynamic reference frame may be positioned relative to the nose 108, thechest of the patient 14, the head of the patient 14, also the dynamicreference frame may be formed as a bite block that may be fitted ontoselected portions of the oral anatomy. Also, the dynamic reference framemay be fitted onto or in a tooth cap that may be fit over a tooth, anoral bite block that may be held within the teeth or jaws of the patientor any other appropriate location.

The dynamic reference frame 54 may either be substantially wireless andpowered by an internal power source or may be wired. For example, a hardwire dynamic reference frame 120 is illustrated in FIG. 9. The hard wiredynamic reference frame 120 includes a bottom body portion 122 and a topbody portion or cap 124. The cap 124 is generally able to mate with thebottom portion 122 in an appropriate manner and may include a recess 126to receive the head of a screw to lock the top 124 to the bottom 122.Formed in the bottom portion 122 is a groove 128 that is able to receivea wire such as twisted pair wire 130. The wire 130 may include leadsthat are soldered to a printed circuit board (PCB) 132. The PCB 132 mayinclude traces that are translated or connected to intermediate wires134 and 136 that are able to transfer power or a signal to and/or from afirst coil 138 and a second coil 140. The coils 138, 140 are generallycoils of wire that generate an induced current by an electric field ormay transmit an electric field.

The line 130 may operatively interconnect the hard wired dynamicreference frame 120 to the navigation interface 50. Therefore, the hardwire dynamic reference frame 120 may transmit the navigation signalsreceived by the coils through the transmission line 130. Alternatively,as discussed above, an internal power source may be provided such thatthe information received by the coils 138, 140 may be wirelesslytransmitted to the navigation controller 34 using known wirelesstechnology.

The hardwire dynamic reference frame 120 may include any appropriatedimensions. For example the hardwire dynamic reference frame 120 may beabout 2 mm to about 10 millimeters in height. Generally, the less theheight of the dynamic reference frame the less the possibility for errorin transmitting the location of the coils relative to the patient 14.Also, the inferior surface at the base 124 may include a radius to matewith a selected anatomical region, such as a forehead.

The hard wire dynamic reference frame 120 may still be fixed to thedermis of a patient 14 in any appropriate manner. For example, thetensioning member 84 may be provided over the top of the top portion 124of the hard wire dynamic reference frame 120. In addition, an adhesivemay be provided on the inferior portion of the hard wire dynamicreference frame 120.

In addition, the hard wire dynamic reference frame 120, particularly theupper portion 124 and the lower body portion 122, may be formed of anappropriate material. For example, materials may include non-conductivematerials such as ceramic or various polymers. In addition, the hardwire dynamic reference frame may be formed of non-conductive carbonfiber materials. In addition, the coils 138, 140 may include conductivecarbon fiber materials as the coil component. In addition, the PCB 132need not be present and the wires may simply be fixed to the coils 138,140 from the lead 130. Nevertheless, various selections may be chosen toinclude the PCB 132 or to wire the lead 130 directly to the coils 130,140.

Therefore, it will be understood that the dynamic reference frame may beformed in any appropriate shape. In addition, the dynamic referenceframe 54 may be substantially moldable or non-moldable depending uponthe selected shape or position for positioning the dynamic referenceframe. Nevertheless, the dynamic reference frame 54 is substantiallypositioned non-invasively on the patient 14. Therefore, rather thanfixing the dynamic reference frame in an invasive manner, such as withbone screws or the like, the dynamic reference frame may be fixed to thepatient in a substantially error reducing manner using the tensioningmembers or a substantially molded portion.

In addition, more than one dynamic reference frame may be provided onthe patient 14. More than one dynamic reference frame may be providedfor error correction or error detection. Nevertheless, the inclusion ofthe non-invasive dynamic reference frames may be allowed forsubstantially simple positioning of the dynamic reference frames duringan operative procedure. In addition, the dynamic reference frames 54 maybe easily positioned relative to the patient 14 in a substantially quickmanner as well. Therefore, the unexpected need for a dynamic referenceframe 54 may be solved by simply fixing the dynamic reference frame 54to the patient 14 using the various constructs. The dynamic referenceframe 54 may also be fixed to the patient 14 in any appropriate manner.Such adhesives may be painted on, sprayed on, or include “double-sided”tape. Regardless, the adhesive allows for simple placement of thedynamic reference frame 54 for a selected procedure.

The size, such as the height, the width, etc. of the dynamic referenceframe may be selected depending upon selected characteristics. Forexample, the hard wire dynamic reference frame 120, which may also besubstantially wireless dynamic reference frame, may include a selectheight that is substantially shallow or low to allow for a reducedpossibility of movement of the dynamic reference frame 120. In addition,the height or distance of the coils 138, 140 from the anatomy of thepatient 14 is small. Therefore, any movement of the hard wire dynamicreference frame 120 is substantially closer to movement of the patient14 than if the coils were positioned further from the patient 14.Therefore, the size of the dynamic reference frame may also be chosendepending upon the selective amount or error of the system.

In addition, as briefly mentioned above, the coils 138, 140 may beprovided in the hard wire dynamic reference 120 or in any appropriatedynamic reference frame. Generally, the coils 138, 140 are substantiallysimilar in functioning to the coils 96 and 98 on the sensor bobbin 90.Simply, the coils are positioned in a slightly different position, butangled relative to one another to provide sensing of six degrees offreedom. Therefore, whether the coils are substantially positioned onthe single member, such as in the sensor bobbin 90, or separated such asthe coils 138, 140 in the hard wire dynamic reference 120, still providethe required information for sensing the location of the dynamicreference frame.

Any of the dynamic reference frames (which also may be wireless) may beused as the dynamic reference frame 54, such as the dynamic referenceframe 70, the intercochealor dynamic reference frame 111, or thehardwire dynamic reference frame 120 may include various selectedcharacteristics. For example, the sensor portion, such as the includedrespective coils, may be removable for various reasons. If an imagingtechnique, such as an MRI is used to image the patient and the dynamicreference frame is left as a fiducial marker, the electromagnetic coilsmay be removed. Therefore, it will be understood that the coils mayeither be permanently included within the dynamic reference frame or maybe removable therefrom, particularly when the dynamic reference frame isused as a fiducial marker.

In addition, the dynamic reference frame may be used as a fiducialmarker. For example, the dynamic reference frame may include a regionthat is substantially matable or molded to mate with a portion of theanatomy in substantially one way. In addition the dynamic referenceframe may also include a portion that is inherently contoured to matewith a portion of the anatomy without including a moldable portion. Thisallows substantially precise replacement and repeatability of placementof the dynamic reference frame to be achieved.

Because of the precise repeatable placement of the dynamic referenceframe it may also serve as a fiducial marker that may be used inpreoperative imaging to be a fiducial marker for use during registrationintra-operatively. Therefore, the dynamic reference frames may includematerials that are substantially radio-opaque or opaque to the imagingprocess. Various materials may be used to form the radio-opaque dynamicreference frames, such as selected metals, selected compounds, andvarious mixtures.

Moreover, if the dynamic reference frame is used as a fiducial marker,it may be selected to include portions on the dynamic reference framethat may be viewed on the preacquired image and during the procedure.For example, as discussed in relationship to the dynamic reference frame70, the dynamic reference frame may include the reference dimple orlandmark 80. It will be understood that a plurality of the referencedimples may be provided on the dynamic reference frame 70 for use duringan operative procedure to reference the patient space to the imagespace. The number of reference points, which either may be physicalportions, such as the dimples, or markings on the dynamic referenceframe, are generally viewable and identifiable on the preacquiredimages, so that each may be matched to a selected portion of the dynamicreference frame during the operative procedure. This allows for multipledegrees of freedom and allows an appropriate and precise registration ofthe patient space to the image space.

In addition, it will be understood that each of the dynamic referenceframes include a portion that allow the dynamic reference frame to beheld relative to the patient 14. Therefore, each of the dynamicreference frames includes a selected holding portion. For example, theholding portion may include the adhesive that adheres the dynamicreference frame to a selected portion of the patient 14. In addition,the moldable portion, such as the moldable portion of the intercochealorimplant 111 a, may be a holding portion and no other portion may beprovided to hold the intercochealor dynamic reference frame 111 relativeto the patient 14. Regardless, each of the dynamic reference frames mayinclude a holding portion that allows the dynamic reference frame to beheld relative to a patient. It may be that the holding portion defines asubstantially matable and repeatable placement of the dynamic referenceframe relative to the patient 14, such that the dynamic reference framemay also be repeatably precisely placed and may be used for variouspurposes, such as a fiducial marker.

Various instruments may be included for use in a selected procedure,such as a stylet 150, with reference to FIGS. 10A and 10B. The stylet150 generally includes a connection wire or cable 152 and an electroniclead and/or handle 154. Extending from the handle 154 is a styletportion 156 that is generally moved within the cavity of the patient 14.For example, the stylet 150 may be the instrument 52 rather than thecatheter. Therefore, the stylet 150 is an exemplary instrument 52.

Generally, the stylet portion 156 includes a distal or tip end 158 and aproximal end 160. The stylet may be positioned through a cannula and maybe used to guide the cannula, though the stylet 150 may be used for anyappropriate reason. Positioned near the distal end 158 is a sensor 162.The sensor 162 may be a coil, or multiple coils, to interact with thefield transmitted by the transmitter coil array 48. Briefly anddescribed in detail herein, the sensor 162 is generally wrapped aroundan internal highly electromagnet permeable core insulated with a heatshrink or any appropriate dielectric material. The details of theprocess and the sensors 162 are described in further detail herein.

With additional reference to FIGS. 10A and 10B, the handle 154 of thestylet 150 may include an area to connect the wires from the coils. Afirst set of contacts 241 provide an area for contact to each of theleads of the first coil 240. A second pair of contacts 245 is providedfor the leads of the second coil 244. In this way, power or sensor leadsmay be attached to the handle or sensor region 154 for receiving thesensitive information of the sensors or coils 240, 244.

With reference to FIG. 11, a probe 166 is illustrated, as a furtheralternative for the instrument 52, and generally includes a handleportion 168 and a probe tip 170. The handle 168 is generally formed of anon-metallic material that can be easily grasped and isolated from theelectrical lead 172. The electrical lead generally provides a current toa portion of the tip 170.

With continuing reference to FIG. 11 and additional reference to FIG.12, a tip sensor 174 may be positioned in the tip 170 of the probe 166.The tip 170 generally is formed of a non-metallic and/or anon-conductive material. Inside of the tip 170 is a metal shaft 176 thatcan be formed of an appropriate electromagnetic permeable material.Formed around the metal shaft 176 is a sensor coil 178. A second sensorcoil 180 may also be provided. The first and second sensor coils 178,180 are generally co-axial and formed along the axis of the permeablerod 176. The tip 170 and the rod 176 with the coils 178, 180 aregenerally positioned within a tube portion 182 of the probe 166. Asdiscussed, the lead 172 provides power to the sensor portion includingthe coils 178, 180. The sensor portion including the coils 178, 180 maybe similar to the sensor portion 162 of the stylet 150 and described indetail herein. Regardless, the sensor portion is generally positionedsubstantially at the tip or the distal end of the probe 166 to allow forsubstantially accurate measurement of the position of the tip of theprobe.

With reference to FIGS. 13 and 14, a suction device 190 is illustrated.Again, the suction device 190 generally includes a handle 192 whichincludes a connection area 194 to be connected to a suction source. Acannula opening 196 runs the length of the suction portion such thatmaterial may be suctioned through a distal tip 198 of the suctioninstrument 190. Also provided through the handle 192 may be a powersource that is able to energize a sensor or sense an electromagneticfield that is acting upon a sensor 200 positioned in the tip 198.

With particular reference to FIG. 14, the suction instrument 190 nearthe tip 198 generally includes an internal ductile and possiblyconductive or nonconductive tube 202. Positioned over the tube is aninner dielectric layer 204. Coils 206 and 208 may also be positionedover the dielectric layer 204. Finally, the sensor 200 may be sealedwith an outer dielectric layer 210. Again, the formation of the sensor200 is described herein including the two coils, 206, 208. Generally,the coils are positioned near the tip 198 of the suction instrument 190and to provide for substantially accurate position data for the tip 198of the suction instrument 190. Therefore, the tip 198 of the suctioninstrument 190 may be moved and the sensor 200 is positionedsubstantially near the tip 198 so that intended or unintended motion ofthe tip 198 relative to the handle may be determined.

The sensors, according to any embodiment described above, are generallypositioned near a distal end or movable end of an instrument, such asthe suction instrument 190, the probe 166, or the stylet 150. Generally,the position of the various instruments, particularly the ends of theinstruments, is determined by the known location of a sensor or atransmitting coil and the known size, length, and other physicalattribute of the instrument. Therefore, the sensor may be positionedaway from or disposed a distance from the extreme end of the instrument.Although a very small and tolerable error may be introduced when theinstruments are flexed or move unexpectedly, but this may also cause theexact location of the tip to not be known. This may require manyrepositioning and attempts to complete a procedure. This error may bedetected or substantially eliminated when the sensor is positioned nearthe distal tip of the instrument, particularly when the instrument isflexible. Therefore, rather than determining or knowing the variousphysical characteristics of the instrument, the actual sensed portion isthe end that may move expectedly or unexpectedly. Therefore, providingthe sensor near the distal tip may provide for substantial accurateposition data of the instrument.

Generally, the position of the instrument is displayed on the display 36and is not generally viewable by a user because it is within the cavityof the patient 14. Therefore, the user is generally dependent upon theaccuracy of the display 36 to ensure the proper location, orientationand other attributes of the instrument relative to the patient 14. Forexample, as illustrated in FIG. 1, the instrument 52, such as thecatheter, is positioned relative to a specific portion of a heart of thepatient 14. Similarly, the stylet 150 may be positioned relative to anextremely particular and precise portion of the brain. Therefore, it maybe selected or desirable to substantially eliminate any error whendetermining the position of the instrument relative to the patient 14.

Although the following description relates generally to the formation ofthe sensor 162 for the stylet 150, it will be understood that the sensormay be used in any appropriate instrument 52, such as the catheter, theprobe 166, the suction instrument 190 or any other appropriateinstrument. In addition, the instruments may include any selected tipshape or sizes depending upon a selected use of the instrument. Forexample, an arthroscope or camera may be provided in the tip for viewingon the display 36 or any other appropriate display. Nevertheless, thesensor may be positioned near the lens portion such that the exact andprecise location of the lenses is known.

In addition, various portions of the instrument may be ductile ormovable such that the tip is not at a fixed location relative to otherportions of the instrument. Therefore, the tip may be movable while thehandle is substantially fixed at a known location. Therefore, the sensorpositioned at the tip is able to provide the position of the tip eventhough the handle has not moved.

It will also be understood that various handle calibration andverification points may be included as well as areas for directingwiring within the various instruments and through the handle. It will beunderstood that these various portions are provided for directingwiring, allowing verification and calibration and are not described inunneeded detail. In addition, the instruments may be substantiallydisposable or reusable, depending upon the various material specificsbeing used and the sterilization techniques.

According to various embodiments, a method of forming the sensors thatcan be positioned near the tip in a substantially small volume or space,such as in the stylet tip 158, is described. With reference to FIG. 9and FIG. 14, the stylet tip 158 is illustrated in detail in FIG. 14.With reference to FIG. 15, a detail of a first sensor coil 240 and anextreme distal tip portion 158A is illustrated. The various coatings orlayers around a central rod 242 is illustrated and described herein.Generally, the central rod 242 is a conductive rod and may includevarious materials such as “302 spring” stainless steel. The material forthe rod 242 that is also generally the flexible or steerable portion ofthe stylet 150 may be any appropriate material. Generally, the materialfor the rod 242, however, is highly permeable to electromagnetic fields.This generally increases the signal to noise ratio or the gain of thesignal of the sent field to a selected amount. Generally, the signal tonoise ratio may be increased at least about 5% depending upon thevarious materials chosen to form the selected construct.

With reference to FIGS. 15 and 16 the stylet tip 158 generally includesa first coil and may also include a second coil 244. The first andsecond coils 240, 244, or any appropriate number of coils may beprovided on the tip 158. In addition, the coils 240, 244 may besubstantially co-axial or formed at an angle relative to one another.That is, the wire or material used to form the coils 240 and 244 may bewrapped at an angle relative to each other around the rod 242. When thecoils are not wrapped at an angle relative to one another, a degree offreedom may not be detected, such as rotation. For various instrumentshowever, such as the uniform stylet tip 158, rotational information maynot be necessary and selectively not determined. Nevertheless, for otherinstruments, such as a suction tube, an ablation tube, or a lens, it maybe desired to produce the coils at an angle relative to one another suchthat rotational direction and location may be determined.

As described in detail in flow chart in FIG. 17, prior to forming acoil, a first dielectric barrier or layer 246 may be provided over therod 242. The first dielectric barrier layer 246 generally is not placedover the extreme end of the tip 158 a and generally includes a back setor offset distance of about 0.025 mm to about 1.5 mm depending upon thesize of the rod 242. For example, the offset distance C may be aselected multiple of a diameter of the rod 242. Not to be limited by thetheory, but including the back-set may reduce the possibility of damageto the first dielectric layer 246 during use of the stylet 150.Generally, the extreme tip 159 a may be used to touch hard surfaces andthis may damage the dielectric material. Nevertheless, it will beunderstood that the first layer of the dielectric material 246 mayextend over the extreme tip of the tip 158.

The coils 240, 244 may then wrapped around the first dielectric layer246. After the coils are positioned over the first dielectric layer 246,a second dielectric layer 248 is provided over the coils 240, 244.Again, the second dielectric layer 248 may be offset a distance D fromthe extreme end of the tip 158 a. Nevertheless, it will also beunderstood that the second dielectric layer 248 may also extend to theend of the tip 158 a.

It will be understood that the first layer 246 and the second layer 248need not necessarily be a dielectric material. This is merely exemplaryand not intended to limit the scope thereof. For example the materialmay simply be used to isolate the windings from an exterior environmentand the first layer omitted entirely. Alternatively, the wire that formsthe coils 240, 244 may be separately or individually coated prior toforming the coils 240, 244. Therefore, the isolation may be achievedwithout forming a separate layer or coating, such as the first andsecond layers 246, 248.

Although the apparatus and a very brief process for forming theapparatus is described above, the following description, in addition tothe flowchart illustrated in FIG. 17, describes a detailed method offorming the stylet tip including the sensor 162 according to variousembodiments. A method of forming a sensor, such as electromagneticsensor that may be either passive or active, is described inrelationship to the flowchart and a method 260. Generally, the methodbegins a start block 262.

After the process is started in block 262, a material may be selectedfor form a core in block 264, such as the core 242. As described above,the selected core material in block 264 may be a highly electromagneticpermeable material. Although it is not necessary that the core be highlypermeable to electromagnetic fields or be conductive, it may bedesirable to provide a highly permeable core for various applications.For example, when forming the stylet tip 158, it may be selected toprovide the stylet tip to have diameter no greater than about 1.25 mm.In addition, it may be selected to include a stylet diameter of lessthan about 1 mm. It may also be desirable to provide a stylet tip 158 inany appropriate diameter or selected property. Therefore, the stylet 158may be deflectable or bendable according to selected characteristics.Also, at the small diameter the highly permeable material may increasethe gain of the field sensed by the coils. Therefore the locationinformation may be more easily determined and sensed.

After the selected core material is chosen in block 264, the core isformed in block 266. The core may be formed according to any selectedspecifications, such as those described above. Therefore, the coreformed in block 266 may include a length, a cross-section, and othervarious properties that may be selected for the stylet tip 158. Althoughthe material may be selected for the core in block 264 and the coreformed in block 266, it will be understood that these steps are optionalas steps for forming the selected sensor. The method 260 is exemplaryfor forming the stylet tip 158. Although the process 260 is exemplaryfor forming the stylet tip 158, it will be understood that variousportions thereof may be used in any process for forming a sensoraccording to the below described process and a tip sensor in asubstantial small area. Therefore, steps that are substantially optionalare positioned in blocks that are outlined with dashed or phantom linesand will be indicated as optional herein. Therefore, it will beunderstood that various steps, although described, are not required toform the sensor as described herein. Therefore, the process is merelyexemplary and various specific details are provided only for clarity andnot intended to limit the description or the appended claims.

After the core is optionally formed in block 266, a first layer ofmaterial is positioned over the core in block 268. The first layer ofmaterial positioned in block 268 may be a dielectric. Though thematerial for the first layer may be any appropriate material and ismerely exemplary a dielectric. The first layer of the dielectricmaterial may be positioned over the core in any appropriate manner. Forexample, the first layer of the dielectric material may be positionedover the core as a heat shrink or shrink wrap process. This being that aportion of the material may be formed as tube and slide over the coreand then shrunk to substantially engage the core along its length.Alternatively, the material may be painted on or sprayed on the coreformed in block 266.

For any or all of these processes, a plurality of layers of the materialmay be positioned on the core to form the first dielectric layer of aselected thickness. The thickness of the dielectric layer may be anyappropriate thickness according to selected characteristics. Forexample, the thickness of the first layer of the dielectric material maybe about 0.00025 inches to about 0.03 inches (about 0.00635 mm to about0.762 mm). Generally, however, the first layer of the dielectricmaterial may be about 0.001 inches (about 0.0254 mm) in thickness.

The dielectric material may also be any appropriate dielectric materialto achieve selected results. For example, it may be selected to havedielectric breakdown strength of about at least about 4,000 volts perabout 0.001 inches (mil) (about 0.0254 mm) in thickness. Although anyappropriate dielectric break down strength may be selected. Also, it maybe selected to choose other properties for the first dielectric layerplaced in block 268. Various materials may be used such as polyestershrink tubing or ULTRATHIN WALL POLYESTER (PET) shrink tubing providedby Advanced Polymers Inc. of Salem, N.H. Although any appropriatematerial may be used, it may be selected to include the dielectricbreakdown strength of at least about 1000 volts per mil.

After the first layer of dielectric material is positioned on the core,the layer may be inspected in block 270. The inspection may be anyappropriate inspection such as a visual inspection, magnificationinspection, or various electrical tests to ensure that the selectedinstallation is achieved. Also, the first layer of dielectric materialmay be inspected to ensure that it has been positioned on the core in aselected manner. As described above, it may be selected to only cover aselected portion of the core and not extend the first layer ofdielectric material substantially to the tip of the core. As illustratedin FIG. 15, it may be selected to position the first layer of dielectricmaterial 246, the distance C from the extreme end 158 a of the tip 158.

After the optional inspection of block 270, a first sensor coil isformed in block 272. The sensor coil, such as the coil 240 illustratedin FIG. 15, may be formed using any appropriate materials. For example,a 48 gauge magnetic wire that is coated with a single built polyurethanewith butyl bonds may be wrapped around the core including the firstlayer of dielectric material to form the first sensor coil.

The wire may be wrapped around the first layer of the dielectricmaterial in any appropriate manner. For example, the coils may bewrapped substantially co-axially with a longitudinal axis of the core.Alternatively, the wire may be wrapped substantially at an angle to thecore for selected reason, such as sensing rotation of the core duringuse. As an example, a first sensor coil may include a first layer ofcoils including approximating 300 turns and a second layer positionedover top of the first layer also having approximately 300 turns.Therefore, the first coil formed in block 272 may include approximately600 turns. Nevertheless, it will be understood that only a single layeror any number of layers may be used and that any appropriate number ofturns may be used to form the first sensor coil in block 272.

The first coil formed in block 272 is exemplary wound around the firstlayer positioned in block 268. It will be understood that the wire usedto form the coil in block 272 may first be coated or may be a coatedwire. When the wire is coated or covered positioning the first layer ofmaterial in block 268 may be omitted. The coating on the wire mayprovide all of the properties, such as electrical, environmental and thelike, that the material in the first layer formed in block 268 mayotherwise provide.

An optional second coil, which may also be formed of coated or coveredwire, may be formed in block 274. Therefore, it will be understood thatany appropriate number of coils may be formed for reasons discussedherein but may include a first coil formed in block 272 and a secondcoil formed in block 274. If there are two coils, the second coil may bepositioned a selected distance from the first coil. For example, thefirst coil may have an edge that is about 0.25 mm to about 10 mm from anend of the second coil. Nevertheless, it will be understood that thecoils may be positioned at any appropriate position on the tip 158 andrelative to one another.

After the first sensor coil is formed in block 272 and optionally thesecond sensor coil in block 274, the ends of the wires forming thesensor coils may optionally be twisted in block 276. The ends of thewires that form the coils formed in blocks 272 and optionally in block274 may be twisted in any appropriate manner. For example, the wires maybe twisted in about 10 to about 30 twist per inch and may be uniformlytwisted rather than twisting one around the other. Although it will beunderstood that the wires may be formed in any appropriate manner andthat twisting the wires in block 276 is merely optional.

After the wires are optionally twisted in block 276, the ends of thecoils are attached to locations on the stylet handle in block 278.Generally, the leads of the coil are attached to selected positions,such as to a printed circuit board or to other wire leads, that allowfor interconnection to various components, such as the navigationinterface 50 (FIG. 1). The coil leads that are attached from block 278may be attached to any appropriate portion and may be from either thefirst sensor coil formed in block 272 or the optional second sensor coilformed in block 278.

After the leads from the coils are attached in block 278, or at anyappropriate time, a second layer of material may be positioned in block280. The second layer of material positioned in block 280 may be anyappropriate material and is only exemplary a dielectric. The secondlayer of dielectric material may be positioned over both of the firstlayer of dielectric material, that was positioned in block 268, and overthe sensor coil formed in block 272, and optionally in block 274. Thematerial that is used to form the second layer of the dielectricmaterial may be the same or different than the material chosen to formthe first layer of the dielectric material in block 268. In addition,the method of positioning the second layer of the dielectric material inblock 280 may also be the same or different that the method used toposition the first layer of dielectric material in block 268. Forexample, the first layer of the dielectric material positioned in block268 may be a substantially heat shrink or shrink tubing that ispositioned over the core formed in block 266 and then shrunk accordingto any selected method, such as heating. Alternatively, the second layerof dielectric material positioned in block 280 may be sprayed or paintedon over. In addition, the material may be the same, such as the UltraThin Wall polyester (PET) heat shrink tubing produced by AdvancedPolymers Incorporated or may be any other appropriate material.

Nevertheless, the second layer of the dielectric material may includethe same or different dielectric break down strength in the first layer.For example, the dielectric breakdown strength of the second layer ofthe dielectric material may be at least 4000 volts per mil or may be anyother appropriate amount.

Briefly, as an example, the first layer of the dielectric material mayprovide insulation between the sensor coil formed in block 272 and thecore formed in block 266. Therefore, the sensor coil formed in block 272is electrically isolated from the core formed in 266. This allows thecore formed in 266 to also be a conductive material and may also act asa core and a gain amplifier for the sensor coil, as described furtherherein. In addition, the second layer of the dielectric material may actas an electrical insulator relative to a patient or a portion exteriorto the core and as an environmental seal to the sensors formed in block272 and optionally in block 274.

It will also be understood that the second layer of the materialpositioned in block 280 may also be omitted. It may be omitted for anyreason, such as the wires that form the coil formed in block 272 arepreviously coated. Therefore, the second layer of material formed inblock 280 may be omitted. Regardless, the second layer of material maybe any appropriate material and need not be a dielectric. The secondlayer of material in block 280 may be positioned for any appropriatereason, such as a liquid seal, an electrical isolation, etc.

After positioning the second layer of the dielectric material in block280 the second layer of dielectric material may be optionally inspectedin block 282. As in block 270, the material may be inspected accordingto any appropriate method, such as visual inspection, magnificationinspection, and electrical testing.

After the second layer of the dielectric material is optionallyinspected in block 282 the ends over the core may be sealed. Asillustrated in FIG. 16, the first layer of dielectric material 246 andthe second layer of dielectric material 248 may not extend over theextreme tip 158 a of the core 242. Therefore, it may be selected to sealthe extreme end 158 a over the dielectric layers 246, 248 to achieve asubstantially water tight or other material tight seal.

The seal formed optionally in block 284 may be formed in any appropriatemanner. For example, the extreme tip 158 a and any selected length alongthe tip 158 may be dipped into a selected material, such as Loctite 4014produced by Henkel Loctite Corp. of Rocky Hill, Conn. The material maysubstantially seal the interior so that no fluid can be wicked or drawntowards the coil 240 through capillary action. Therefore, the coating ofthe dielectric layers, blocks 268 and 280 may be sealed in anyappropriate manner to ensure that no fluid is allowed to destroy orshort the coils formed on the tip 158.

In addition to the steps described above, various other steps such astesting the dielectric strength in block 286, testing the connection ofthe coil after attaching the coil leads in 278, testing the coils inblock 288, and inspecting the construct for achieving the appropriatedimensions in block 290 may be performed. Then the process ends in block292.

Although various optional steps may have been performed in the method260 it will be understood that the sensors generally formed bypositioning on a first layer over dielectric material over a core,forming a sensor coil around the first layer of the dielectric materialin block 272, and positioning a second layer of dielectric material inblock 280 over the coil may be performed. In addition, the dielectricmaterials may be any appropriate materials and are generally providedonly for safety considerations. Therefore, simply forming the coilaround the core may be performed for any appropriate purpose. Providingthe dielectric layers are able to protect the user and the patient fromany possible surges and insure that the instrument is not corrupted byenvironmental degradation.

Furthermore, additional assembly steps may be performed depending uponthe selected instrument. As illustrated in FIG. 10, the cable 152 may beinterconnected with the connection area 154 and interconnected with thenavigation probe interface 50. Alternatively, if the other instruments,such as the probe 166 or the suction tube 190 are formed, the relativehandles may be provided and affixed thereto and various otherconnections may also be performed. Nevertheless, it will be understoodthat these steps are not necessary for forming the sensor near the tipof the construct.

With reference to FIG. 16 the exterior dimension or diameter E of thetip 158 and of the stylet portion 156 of the stylet 150 may be anyappropriate dimension and may be about 0.09 mm to about 1.5 mm indiameter. It will be understood that the dimension may be anyappropriate exterior dimension as the stylet portion 160 may be formedin any shape, but may be a cylinder. The diameter E generally includesthe dimension of the core 242 the first dielectric layer 246 and thesecond dielectric layer 248. In addition, a diameter F that includes thediameter or size of the coil 240 may be about 0.9 mm to about 1.50 mm indiameter. Therefore, the diameter F may be greater than the diameter Edepending upon whether the space between the coils is selected to beequal to the size as around the coils 240.

Regardless of the actual size, it is desired to include a diameter ofthe stylet portion 156 that is substantially small for use in variouspurposes. For example, the stylet portion 156 may generally be providedwith a cannula that is positioned in various portions of the anatomy,such as the brain. Therefore, it may be desirable to provide the styletportion 156 and a plurality of other instruments through the cannulawithout moving the cannula. Therefore, the stylet may be of a selecteddiameter that will substantially freely move within the cannula.

Although it may be selected to keep the maximum diameter F under aselected size, it will be understood that any appropriate or selectedsize of diameter may be used. Simply having a substantially smalldiameter may provide various selected properties, as having it selectedfor various instruments and purposes. Again, as described above, variousportions of the instrument and the method may be optional and notnecessary. Although the core 242 may be formed of a substantiallyconductive material that is surrounded by the first layer of dielectricmaterial 246, that is able to isolate the coil 240 from the conductivematerial of the core 242, and the second layer of dielectric material248 provided to enclose the coil 240 from an exterior environment; itwill be understood that various other portions, such as providing thecore 242 as the core 176 in the probe 166 or the metal tube 202 on thesuction instrument 190 may also be provided.

The core 242 may be formed of any appropriate material, but may beformed of the permeable material that may include ferrous materials suchas ferrites like those provided by Fair-Rite Products Corp. of Wallkill,N.Y. The permeable material may provide a gain to the signal of thecoils, such as the first coil 240 and the second coil 244 in the stylet150. The material may provide a gain that is relative to itspermeability, especially above the permeability of air. Therefore, thegain experienced may be dependant upon the type of material chosen forthe core 242, or any core about which the coils are formed in variousembodiments.

In addition, it will be understood that any appropriate number of coilsmay be provided. For example, the stylet 150 may include the first coil240 and the second coil 244. As described above, the windings of thecoils 240, 244 may be substantially co-axial so that only five degreesof freedom are determined. Nevertheless, the windings of the coils mayalso be formed at an angle relative to one another so that rotationalorientation of the stylet 150 may also be determined. In addition, anyappropriate number of coils may be provided along the length of theinstrument for various purposes.

For example, two coils that are coaxial may be provided for errordetection. The first coil may be provided at a known distance from asecond coil. Therefore, the sensed position of the first coil 240relative to the second coil 244 may be used to detect errors between thepositions of the two to determine the exact location of the tip 158 ofthe stylet 150. In addition, a compensation circuit may be provided tocompensate for the sensed signal from the first coil 240 relative to thesecond coil 244. Therefore, providing two coils in the stylet 150 may beprovided for any number of reasons or for all appropriate reasons. Inaddition, it will be understood that the number and types of coils maybe provided in each of the instruments described above and any otherappropriate instrument. Nevertheless, a substantially small or narrowsensor coil may be provided according to the steps described above andmay also be provided according to the various optional steps describedabove.

With reference to FIGS. 1 and 18 the isolator circuit 55 may be providedto isolate any portion of the instrument 52 that may engage the patient14 from the electrical source, such as the work station 34. Asillustrated in FIG. 1, the instrument 52, which may include the stylet150, the probe 166, the suction instrument 190, and/or any otherappropriate instrument, is inserted into the patient 14. Each of theinstruments may include the sensor 58, as disclosed herein and above, towhich an electrical current has provided. In addition, the dynamicreference frame 54, according to any of the embodiments or various otherembodiments, as described herein or understood to be included within thescope of the present disclosure, may also includes an electrical leadfrom the navigation probe interface 50. In addition, any other systemssuch as the probe 66 may each have an electrical current providedthereto. The isolator circuit 55 may be positioned anywhere to isolateany of these instruments from the electrical source.

The isolator circuit 55 may include any appropriate isolationtransformer 300. The transformer 300 may include a first coil 302 thatis operable to transmit or receive a signal. The first coil 302 maygenerally be on an output side that receives a signal and transmits itthrough the navigation probe interface 50 and to the workstation 34 orthe coil array controller 48.

The first coil 302 may be separated from a plurality of second coils 304a, 304 b, and 304 c by a dielectric or appropriate medium 306. Asdescribed herein each of the coils 304 a-304 c may be in-line with aselected instrument or device. It will be understood, however, that asingle second coil may be provided with a plurality of taps connectedthereto. The dielectric medium 306 eliminates a current that may attemptto transfer from the first coil 302 to the second coils 304 a, 304 b,and 304 c or vice versa. Nevertheless, an electromotive force may beprovided into either of the first coil 302 or the second coils 304 a,304 b, and 304 c that may couple across the dielectric material 306. Inthis way, the second coils 304 a, 304 b, and 304 c is electricallyisolated from the first coil 302, such that only a potential is able totransfer across the dielectric medium 306.

The second coil 304 may include leads to the dynamic reference frame 54,the instrument 52, such as a catheter, and the probe 66. As discussedabove the instrument 52 may also be the stylet 150, the probe 166,and/or the suction tube 190, or any appropriate instrument. Both thefirst coil 302 and the second coils 304 a, 304 b, and 304 c may alsoinclude a ground lead. Generally, the first coil 302 is operablyconnected to the work station 34 through the navigation probe interface50. The navigation probe interface may include appropriate power sourcesand amplifiers as necessary. Therefore, the navigation probe interface50 may be electronically isolated from the various portions of theassembly 10 that may engage the patient 14. In this way, a current maynot be transferred through the electrical isolator 55 to any of theinstruments, sensors, or portions that touch the patient, such as theinstrument 52 and the dynamic reference frame 54.

In addition, as discussed briefly below, the first coil 302 may includea different number of windings than the second coils 304 a, 304 b, and304 c. For example, if it is desired to include a stronger signal goingback to the navigation probe interface 50, a number of windings in thefirst coil 302 may be greater than the number in the second coil 304.Therefore, the electrical isolator 55 may also act as an amplificationcircuit for receiving a signal from the various components, such as thedynamic reference frame 54 and the instrument 52.

As illustrated in FIG. 1, the isolator circuit 55 may be provided on anyof the lines from the navigation probe interface 50. Therefore, anyelectrical surge may be immediately stopped before engaging the patient14 or instrument 52. Thus, the isolator circuit 55 may be positioned oneach of the lines leading to each of the instruments, the probe 66 orthe dynamic reference frame 54. Furthermore, the isolator circuit 55 maybe incorporated into the navigation probe interface 50 or into any ofthe instruments 52, the dynamic reference frame 54, or the probe 66. Theisolator circuit 55 may be positioned anywhere to eliminate the currentthat may be unintentionally provided to the patient 14.

For example, with reference to FIG. 9B, the isolator circuit may beincluded within the circuit capsule 154 of the stylet 150. Therefore,the power provided to the stylet 150 may be interrupted when a selectedvoltage or current is reached. The isolator circuit may allow stopping avoltage before it is able to pass through the circuit to reach thesensors. The isolator circuit 55 in addition to the dielectric layerspositioned over the coils 240, 244, may assist in protecting the patient14 from undesired electrical shock. In addition, the isolator circuit 55may be incorporated into any other appropriate portion of the otherinstruments with a dynamic reference frame.

In addition to isolating the patient 14 from undesired electricalcurrent or shock, the isolator circuit 55 may also act as an amplifierto increase the signal to noise ratio. For example, the isolator circuit55 may be a step up transformer that is designed to increase the signalto noise ratio a selected amount. For example, a selected side, such asthe signal output side, of the circuit may include a number of windingsthat is greater than the signal input side such that the signal isstepped up and the signal to noise ratio is increased. Therefore, theisolator circuit 55 may not only electrically isolate the patient 14from an undesirable surge, but may also increase the signal to noiseratio to increase the efficiency of the navigation system 10.

Therefore, the navigation system 10 may be provided to include a dynamicreference frame 54 that is substantially non-invasive such that thepatient 14 does not endure further trauma than required from theoperative procedure. Generally, the navigation system 10 is able toprovide a less invasive or minimally invasive procedure to achieve lesstrauma to the patient 14. Therefore, providing a substantiallynon-invasive dynamic reference frame may assist in decreasing theoverall trauma or invasiveness of the procedure.

In addition, the sensor coils may further reduce the size of theinstrument for various purposes. In addition, the size of the coils mayallow the coils to be positioned near the distal end of the instrumentto more precisely determine the position of the instrument. Therefore,the position determination of the instrument can be more accurate. Forexample positional accuracy can be increased by at least about 5% overplacing the sensors away from the tip. The procedure may then beperformed with fewer attempts thereby again further reducing thepossible trauma of the procedure.

Also, the isolator circuit 55 may increase the signal to noise ratio tobetter determine the position of the various sensors and thereforedetermine the position of the instrument. In addition, the isolatorcircuit 55 may assist in isolating the patient 14 from any electricalsources of the navigation system 10. Therefore, the navigation system 10may increase the efficacy.

According to various embodiments dynamic reference frames (DRFs) may beprovided. DRFs may include a tracking sensor. The tracking sensor may betracked by a tracking system. The DRF may be used by the system toregister or maintain registration of patient space to image space.

Various DRFs may be fixed or inserted in various portions of theanatomy, such as those described above and herein. Various DRFs may befixed in bores in hard or boney portions. Various DRFs may be fixed inat least one orientation relative to selected portions of the anatomy.It will be further understood that although a DRF is discussed inparticular herein, any appropriate sensor may be provided. The sensormay be a portion of a tool, a probe, or any other instrument. Also theDRF, according to various embodiments may include coils for use in anelectromagnetic tracking system, but may also include or alternativelyinclude optical sensors, acoustic sensors, or any appropriate sensorportion. The DRF may be also referred to as a DRF assembly. The sensorin the DRF may generally be referred to as a tracking sensor for us in aDRF or a DRF sensor. Thus, it will be understood, that a DRF may includea DRF sensor that includes a tracking sensor used as a DRF.

Further, as described above and herein, a plurality of the DRFs may beused to assist in maintaining registration of the patient space to theimage space. As described above, the registration allows for thetracking system to track an instrument relative to the patient andensure that the display shows an accurate position and orientationrepresentation of the instrument relative to the patient. The DRFs, asdescribed above, assist in maintaining the registration of the patientspace to the image space during a selected procedure regardless ofmovement of the patient. It will be understood, however, that anyappropriate number of DRFs may be provided on the patient or in aselected position for maintaining the registration of the patient spaceto the image space.

For example, a single DRF that provides six degrees of freedominformation may be used. The single six degree of freedom DRF (6 DOFDRF) tracks six types of movements in space that may be identified withthe single DRF and maintained relative to the patient. Generally, the 6DOF DRF is substantially fixed both rotationally and translationallyrelative to a portion of the patient. For example, an anti-rotation DRFmay be positioned relative to the patient, such as in a bony portion,that includes a selected number of tracking sensors or coils to ensurethe 6 DOF DRF. In this regard, three coils, positioned for example,orthogonal to one another will provide 6 degrees of freedom information.

Nevertheless, more than one DRF may be provided if a selected type ofmotion is not fixed or trackable. For example, a rotational movement maynot be fixed and therefore at least one degree of freedom, or one typeof motion may not be tracked by the tracking system. Therefore, it maybe selected to include more than one DRF to allow for determination ofthe type of movement not detectable by the single DRF but may becompared between a plurality of the DRFs to determine the last type ofmotion. Alternatively, the single DRF may only include two orthogonalcoils and still be rotationally fixed to the patient. However, use ofthe two coils generally will not provide 6 degrees of freedominformation.

In this regard, generally in an electromagnetic tracking system, threecoils substantially unaligned with one another, such as orthogonal toone another, are required to provide six degrees of freedom information.These coils or tracking sensors may be located in a single DRF.Alternatively, three DRFs, where each each DRF includes a single coil,where each coil is again not positioned coaxial or linear relative tothe other coils. This combination will also provide six degrees offreedom information. By providing less than three coils within a singleDRF enables the DRFs to be smaller due to requiring less coils andhence, overall smaller size. Therefore, a single six degree of freedomDRF would generally be larger than individual DRFs each providing only asingle coil and three degrees of freedom information. The size of theDRFs may assist in positioning the smaller DRFs relative to a selectedportion of the anatomy. This may be useful when positioning the smallerDRFs in substantially tight or small areas, such as under a small tissueportion relative to the cranium or any selected portion of the anatomy,such as cervical vertebrae. Nevertheless, the smaller DRFs would be usedfor any appropriate purpose.

With reference to FIG. 19, a tracking sensor that can also operate as aDRF 350 is illustrated. The DRF 350 generally includes a tracking sensorthat can be tracked with a tracking system. The DRF 350 may bepositioned relative to a bone or anatomical portion 352. The bone may beany appropriate bone, such as a femur, humerus, etc. For example, a bore354 may be formed in the bone 352 to receive at least a portion of theDRF 350. The DRF 350 may include a wired portion 356, which may providepower to the DRF 350 or transmit a signal from the DRF 350. It will beunderstood, however, that the DRF 350, or any appropriate DRF discussedabove or herein may be substantially wireless. For example variouswireless channels may be used to transmit or receive information.Various internal power sources may be provided, such as an internalbattery. A power signal may be used to apply remote power to the DRF,and an LC Tank circuit may be used to transmit a signal. Variousexemplary wireless DRFs are described in U.S. patent application Ser.No. 10/245,843, entitled, “SURGICAL COMMUNICATION AND POWER SYSTEM”,filed Sep. 22, 2002; and U.S. patent application Ser. No. 10/837,997,filed May 3, 2004, entitled, “METHOD AND APPARATUS FOR IMPLANTATIONBETWEEN TWO VERTEBRAL BODIES”, each of which is incorporated herein byreference. The DRF 350 may be any appropriate sensor, such as anacoustic sensor, an optical sensor, an electromagnetic sensor, or acombination thereof. Regardless, the DRF 350 may be positioned in thebore 354 to substantially receive the DRF 350, such that it can be fixedrelative to the bone 352.

Positioning the DRF 350 in the bore 354 may eliminate or reduce the needfor other attachment mechanisms to provide for a fixed position of theDRF 350 relative to the bone 352. For example, various pins,interference portions, and the like may be used to interconnect the DRF350 with the bone 352. For example, various screws, pins, interferenceportions, and the like, may be provided and connect the DRF 350 with thebone 352. Also, in addition to or alternatively to the pins, the DRF 350itself may be formed in an interference shape such as a square,polyhedron, etc. The various geometries may interact with the bore 354to resist or eliminate rotation of the DRF 350. Nevertheless, the use ofthe bore 354 may assist in assuring the DRF 350 does not move relativeto the bone 352, whether or not various other interconnection portionsare used. It will be understood, however, that the bore 354 may both fixand reduce an exposed profile of the DRF 350.

Further, it will be understood that the DRF 350 need not include thewire 356. For example, the DRF 350 may be substantially self powered orpowered by an external source or signal. Therefore, the wire 356 may notbe necessary and the DRF 350 may be provided in the bore 354 alone.

In addition, the bore 354 may allow the DRF 350 to be positionedrelative to the bone 352 and be provided below or underneath a surfaceof soft tissue 360. Therefore, the DRF 350 may be a substantiallysub-dermal or sub-soft tissue DRF. This may allow the DRF 350 to bepositioned in the bone 352 and remain in the bone 352 while notaffecting a soft tissue 360 that may be positioned next to the bone 352.This may also assist in providing a substantially normal operation, suchas a range of motion, of the bone 352 with the soft tissue 360 in place.in this case the profile or shape of the DRF 350 may be made to reduceor eliminate any sharp edges or surfaces to prevent the DRF 350 frominterfering with the soft tissue 360.

Nevertheless, as discussed above, the DRF 350 may be tracked accordingto various procedures to allow for a determined position of the DRF 350.Therefore, movement of the bone 352 may be tracked with the DRF 350 evenwhile soft tissue portions, such as the soft tissue 360, surrounds or ispositioned relative to the bone 352. Keeping or positioning the softtissue 360 near the bone, in a generally natural orientation, may allowfor obtaining a substantially natural motion of the bone 352.

With reference to FIGS. 20-24, various DRFs according to variousembodiments, may include mechanisms to reduce rotation or otherunselected movement of the DRF relative to a selected portion, such as aportion of the anatomy. Further, it will be understood that the DRFsensor, as a part of the DRF, may be positioned at any appropriateposition relative to the anatomy or any other portion to which it isfixed. Therefore, it will be understood that DRFs, according to thevarious embodiments may include mechanisms or apparatuses that fix theDRF in a selected orientation or position relative to an anatomy, orother appropriate portion.

Various DRFs according to various embodiments, may include the DRF orDRF assembly 370, illustrated in FIG. 20. The DRF 370 may include a DRFsensor portion 372 that may be a substantially optical DRF, anelectromagnetic DRF, and acoustic DRF or the like. Nevertheless, the DRFsensor 372 may be provided with the DRF 370 in a substantially anti- orreduced rotation mechanism. The DRF sensor 372 may include a wiredportion 374, as discussed above. Nevertheless, also as discussed above,the DRF sensor 372 may be substantially wireless and include a powersignal or be internally powered, such as those discussed above.

The DRF sensor 372 may be attached to a connection portion 376 thatincludes a first arm or leg 378 that is hingedly or movablyinterconnected with a second arm or leg portion 380. The first legportion 378 may be movable relative to the second leg portion 380 with amovement mechanism 382. The movement mechanism 382 may be anyappropriate mechanism, such as a screw that interconnects a boss 384extending from the first leg 378 with the second leg 380. Therefore,movement of the screw 382 may move the first leg 378 relative to thesecond leg 380. In this way, the two legs 378, 380 may be moved andlocked or fixed relative to one another to form an engagement relativeto a selected surface, such as a spinous process of a vertebra of thespine. In addition, the legs 378, 380 may include further engagementportions 386 that assist in holding the DRF 370 relative to a selectedposition. For example teeth or spikes may be included as the engagementportions 386 to bite into or fixedly engage the anatomy, such as aspinous process S. In addition, the screw 382 may be operated with anyappropriate mechanism, such as with a tool, substantially manuallyoperated, or the like.

Nevertheless, the DRF 370 may be positioned relative to a selectedportion of the anatomy, substantially in a manner that reduces oreliminates rotation of the DRF 370. As discussed above, various degreesof freedom of the DRF 370 such as six degrees of freedom (6 DOF), toassist in determining its location, may be determined using varioustechniques. The accuracy or efficacy of the determined locations may bereduced if the DRF 370 is allowed to rotate relative to a selectedportion. Therefore, various mechanisms, such as the first leg 378 andthe second leg 380 that may be positioned relative to one another, mayassist in reducing or eliminating the rotation of the DRF 370. Fixingrotation of the DRF 370 may assist in assuring that substantially anymovement of the DRF 370, such as the DRF sensor 372, may be due to theportion to which the DRF 370 is attached and not to motion of the DRF370 itself.

With reference to FIG. 21, a DRF or DRF assembly 400 is illustrated. TheDRF assembly 400 may include a DRF sensor 402, a DRF connection portionor anti-rotation portion 404 and an interconnection portion or member406. Generally, the DRF sensor 402 may include a casing that surroundsthe sensor portions of the DRF sensor 402. Nevertheless, theinterconnection portion 406 may include a shaft 408 defining a thread410. The thread may engage a portion of the connection member 404 as tosubstantially fix the DRF sensor 402 relative to the connection portion404. The connection portion 404 may also include a first leg 412 and asecond leg 414. The two legs 412, 414 may engage two sides of a selectedstructure, such as a spinous process S of the spine (FIG. 21A). In thecase of engaging a spinous process, the threaded portion 410 may bothengage one or both of the spinous process and the connection member 404.

Regardless, the interconnection with the connection member 406 mayassist in holding the connection member 404 relative to the selectedportion of the anatomy. The two legs 412, 414 may allow for at least twopoints of contact to resist movement of the DRF sensor 402, such asrotational movement thereof, relative to a structure of the anatomy.Therefore, the DRF 400 may be positioned relative to a portion of theanatomy while substantially reducing a selected motion of the DRF 400relative to the anatomy. As discussed above, position information of theDRF 400 may be used to determine a location of a selected portion of theanatomy, such as a spinous process or a vertebra.

As exemplary illustrated in FIG. 21A, each of the legs 414, 412 mayengage or contact a selected side of the spinous process S. The legs mayfurther include engagement portions to bite into or fixedly engage thespinous process S. Further, the screw may be screwed into the spinousprocess to lock or fixedly engage the DRF 400 together. The screw mayengage the sensor portion 402 relative to the member 404 to hold thesensor 402 in a selected position. Also the sensor 402 may be keyed,such as with the member 404, such that it may not rotate relative to thelegs 412, 414.

With reference to FIG. 22, according to various embodiments, a DRF orDRF assembly 430 is illustrated. The DRF assembly 430 may include a DRFsensor portion 432, which may include or provide a DRF sensor. The DRFsensor may be any appropriate tracking sensor, such as an opticalsensor, an acoustic sensor, an electromagnetic sensor, or anyappropriate sensor. The DRF assembly 430 further includes an engagementportion or member 434, such as a member to engage a selected portion ofthe anatomy. A further connection portion 436 is provided tointerconnect the DRF sensor 432 with the connection member 434.

The interconnection portion 436 may include a shaft 438 that defines athread 440. The shaft 438 may pass through a bore 442 formed in thesensor portion 432 to engage or pass through the attachment member 434and engage a selected portion of the anatomy, such as a bone. Inaddition, the connection portion 436 includes a surface or structure 444that may interconnect or mate with a second surface or structure 436defined by the connection portion 434. Therefore, the DRF sensor 432 maybe held fixed relative to the connection portion 434 in a selectedmanner and/or orientation. Further DRF sensor 432 may be keyed orinclude portions to engage the member 434 to resist or eliminaterotation relative to the member 434.

In addition, the connection member 434 may include a first leg portion448 and a second leg portion 450 that may allow for at least two pointsof contact with a selected portion. For example, the two portions 448,450 may engage either side of a spinous process to assist in holding theDRF assembly 430 relative to the spinous process, for example similar tothe legs 412, 414 in FIG. 21A. The portions 448, 450 may assist inreducing or eliminating rotation of the DRF assembly 430, including theDRF sensor 432, relative to the anatomy or other structure. Therefore,the threaded portion 440 may engage a portion of the anatomy compressingthe connection portion 436 to interconnect the first structure 444 withthe second structure 446. In addition, the first portion 448 and thesecond portion 450 may engage two sides or two points relative to aselected portion of the anatomy for assisting and holding the DRFassembly 430 relative thereto in a substantially immovable manner.

As discussed above, the DRF assembly 430, including the DRF sensor 432,may assist in determining a position of the DRF assembly 430 and aportion to which it is interconnected. Therefore, reducing a motion ofthe DRF sensor 432 relative to a selected member may increase theaccuracy, the efficacy and the degrees of freedom of the sensed movementor position of the member to which the DRF assembly 430 is attached.

With reference to FIG. 23, a DRF assembly 460 is illustrated. The DRFassembly 460 may include a first portion 462 that may define or includea DRF sensor 464. As discussed above, the DRF sensor 464 may be anyappropriate sensor, such as an optical sensor, an acoustic sensor, anelectromagnetic sensor, or combinations thereof. Similarly, as discussedabove, the DRF sensor 464 may be substantially wired or wirelessaccording to various embodiments.

The first portion 462 may extend or be interconnected with a secondportion or shaft portion 466. The first portion 464 may be substantiallyfixedly attached to the shaft portion 466 or may be removable therefrom.The shaft portion 466 may extend from a base portion 468 that isoperable to interconnect with a selected member, such as a portion ofthe anatomy including a cranial or spinal region. Therefore, the shaftmember 466 and/or the base member 468 may be implanted at a selectedtime and the first portion 462 may be interconnected with the shaft 466at a selected later time. Further, it will be understood that the shaft466 and/or the base 468 may be provided as fiducial markers. Theseportions may be inserted as markers for use in pre-operative imaging andused as fiducial markers for registering the images before or after theDRF 462 is attached.

The base portion may include one or a plurality of anti- or reducedrotation members 470. The anti-rotation members 470 may engage a member,such as an anatomical structure, including a bone, off center from acentral axis defined by an attachment mechanism 472, such as a screw.The screw 472 may interconnect the base 468 with a selected portion ofthe anatomy, while the anti-rotation pins 470 interconnect the base 468with the anatomy at a different axis. Therefore, rotation around theaxis of the screw 472 may be substantially reduced or eliminated. Itwill be understood that a plurality of the anti-rotation pins 470 may beprovided according to various embodiments.

Also, the shaft 466 may be provided in a plurality of lengths dependingupon various applications. For example, the shaft may include a lengthof one centimeter or less for various low profile or percutaneousapplications. Other applications may use a longer shaft, such as a shaftgreater than about one or two centimeters for various applications, suchas connection to a spinous process or a cranial portion. Regardless, theanti-rotation pins 470 may assist in eliminating rotation of the firstportion 462, including the DRF sensor 464 relative to a selected portionof the anatomy, such as a bony portion.

In addition to the anti-rotation pins 470, or alternatively thereto, thebase 468 may also define a spike or projection 474. The spike 474 mayengage the member, such as a bony structure at an axis different fromthe axis of the screw 472. The may also assist in reducing rotation orrotational tendencies of the DRF assembly 460.

The spikes 474 may be molded into the base 468 to first engage aselected portion, such as a bony portion. After preliminary engagement,the separate of modular anti-rotation pins 470 may be passed through thebase 468 to further assist in reducing rotation of the DRF assembly 460.Therefore, it will be understood that the DRF assembly 460, or anyappropriate DRF assembly, may include one or a plurality ofanti-rotation mechanisms.

With reference to FIG. 24, a DRF assembly 490 according to variousembodiments is illustrated. The DRF 490 may include a body portion 491defining a first leg 492 and a second leg 494. A connection mechanism496 is provided to interconnect the DRF 490 with a selected portion,such as a portion of an anatomy.

The connection mechanism 496 may define a thread 497. The thread 497 mayengage threads defined by the body 491. The connection mechanism mayfurther engage the anatomy. Also, the legs 492, 494 may include astructure 498 operable to engage a portion of the anatomy. A spike orfurther fixing member 499 may extend from the legs 492, 494 to engagethe anatomy.

The connection mechanism 496 may be used to connect the body 491 to theanatomy. As discussed above, according to various embodiments, each ofthe legs 492, 494 may engage a different portion of the anatomy toresist rotation or other movement of the DRF 490. This may hold a DRFsensor portion in a selected position relative to the anatomy. The DRFsensor portion may be included in the body 491, the connection mechanism496, or connected to either. For example, after positioning the DRFassembly 490, a DRF sensor may be fit to the connection mechanism 496.

It will be further understood that a DRF or other instrument may includeone or a plurality of anti-rotation mechanisms according to variousembodiments. Therefore, the DRF need not include only a single or smallcombination of anti-rotation mechanisms, but may include a plurality ofmore than one anti-rotation mechanism. Further, as briefly discussedabove, various anti-rotation mechanisms may be selected based uponvarious applications. For example, a DRF to be interconnected with aspinal portion, such as a spinous process, may include variousanti-rotation mechanisms, while various other DRFs may include differentanti-rotation mechanisms.

With reference to FIG. 25A, an instrument 520 that may include atracking sensor 522 is illustrated. The tracking sensor 522 may bepositioned in any appropriate position, such as in a handle portion 524.The tracking sensor 522 allows the instrument 520 to be tracked suchthat a location of the instrument 520 or a member to which is connectedcan be tracked. The tracking sensor 522 may be any appropriate trackingsensor, such as an electromagnetic sensor, an optical sensor, anacoustic sensor, or the like. Nevertheless, the tracking sensor 522 maybe positioned in the handle 524 or any appropriate portion relative to ashaft or extension portion 526.

The shaft 526 may include a fitting or connection end 528. Theconnection end 528 may include a locking or spring paddle portion 530.The attachment portion 530 may include a flexible or deformable member532 that may flex or move relative to the shaft 526 through a flexing orhinge area 534. The inner connection portion 530 may allow theinstrument 520 to be interconnected with a selected instrument or tool,such as a cutting block 540 (FIG. 26), in a desired orientation.

The tracking sensor 522 interconnected in the instrument 520 may be usedto sense a position of the instrument 520 relative to the tool 540. Forexample, the length of the shaft 526 or an orientation of the shaft 526,may be known relative to a selected portion of the shaft, such as theinterconnection portion 530. Thus the location and orientation of thetracking sensor 522 relative to the tool 540 is known. This knownorientation and location can be used to assist a user, such as asurgeon, in a procedure, such as an orthopedic procedure. For example,the tool 540 may be a cutting block to be oriented for a selectedresection.

With reference to FIG. 25B, an instrument 520′ may include a shaft 544that includes a bent or angled portion 546. The instrument 520′ maystill include the tracking sensor 522 in the handle or operable portion524 for positioning or operating the instrument 520′. Further, theinstrument 520′ may include an attachment region 530 similar to theattachment region 530 of the instrument 520′. The bent portion 546,however, may allow for positioning of the instrument 520′ in a selectedposition that may not allow for a substantially straight shaft. Inaddition, the bent shaft 544 may allow for an efficient use of theinstrument 520′, such as easy viewing of a surgical area or movement ofselected instruments, such as a minimally or less invasive surgicalprocedure.

Regardless of the configuration selected for the shaft 526 or anyappropriate shaft portion, such as the shaft 544, the instrument 520 maybe fit relative to the tool 540 that may be a cutting block, asillustrated in FIG. 26. For example, to resect a selected portion ofanatomy, such as a tibia 550, the cutting block 540 may be positionedrelative to the tibia 550. The cutting block 540 may be held relative tothe tibia 550 in any appropriate manner. For example, a pin 552 or aplurality of pins 552 may be provided to fix the cutting block 540 in aposition relative to the tibia 550.

In a surgical navigation system, such as the system described above, itmay be desirable to assure that the cutting block 540 is positioned at aselected position, orientation, etc. The instrument 520, including theinterconnection portion 530, may be positioned relative to the cuttingblock 540. For example, the cutting block 540 may include a guide orcutting slot or surface 554 defined by the cutting block 540. Theinterconnection portion 530 of the shaft 526 may be fit into the guideslot 554 to hold the instrument 520 relative to the cutting block 540.It will be understood that the interconnection region 530 may be anyappropriate interconnection region and is not limited to a spring member532. For example, various deformable legs, quick-release screws, and thelike may be used to efficiently interconnect the instrument 520 with aselected member.

Once the instrument 520 has been fit in the cutting block 540 thetracking sensor 522 may be used to determine a location and orientationof the guide slot 554 of the cutting block 540. This may assist ininsuring that the cutting slot or guide surface 554 is positionedrelative to the tibia 550 in a selected position, such as a pre-selectedor planned position.

Therefore, the instrument 520 may assist in positioning or determining aposition of the cutting block 540 relative to a selected portion of theanatomy. This may also allow a user to determine a cutting plane and thecutting plane may be displayed for use by a user. The instrument 520 maybe used without pre-selecting or knowing the position or type of cuttingblock 540. Thus any appropriate cutting block 540, or other tool, may beused with the instrument 520 to ensure a proper or planned location,orientation, angle, etc. is obtained without including the trackingsensor 522 on the tool 540.

The instrument 520 may be inserted into the tool 540 before fixing thetool relative to the patient, as well. This may allow a representationof the tool 540 to be displayed relative to the patient 14 on thedisplay. This may allow the tool 540 to be positioned in a substantiallyplanned or selected position, for example in a less or minimallyinvasive procedure. The user may use the display with the representedtool 540 to ensure that the selected location, orientation, etc. isachieved before or while fixing the tool to the patient or using thetool 540. Also, the plane of the cut may be displayed on the display 36prior to the cut being formed.

It will be understood that the instrument 520 may be used with anyappropriate tool, such as a cutting block for cutting various otherportions of the anatomy, other than the tibia 550. For example, theinterconnection region 530 may be interconnected with the cutting blockfor selecting a cut in a spinal area. In addition to determining theposition of the cutting slot 554, or any appropriate cutting slot, theinstrument 520 may be used to determine an orientation of the cuttingguide 554 relative to a selected surface. For example, as discussedabove, the tracking sensor 522, may be used to determine an angle of aselected portion, such as the cutting guide 554, relative to theanatomy. Further, the instrument 520 may be used to determine a depth orlength to be formed with the guide 540.

In addition, the interconnection region 530 allows for a substantiallyefficient connection of the instrument 520 to a selected portion, suchas the cutting block 540. As discussed, the connection portion 530 maybe any appropriate interconnection region 530. For example a screw, apin, or the like may be used. Regardless, the instrument 520 may allowfor the navigation of the tool 540 without including a sensor on thetool 540. Thus, the tool 540 need not include the bulk of the sensor orbe specially made to include the sensor for use with the tracking system44.

The interconnection portion 530 may allow for a hands-free or singlehand operation of the instrument 520. Once positioned, the instrument520 may be held relative to the cutting block 540 with no additionalneed for intervention by a user. Therefore, the instrument 520,including the tracking sensor 522, may be positioned in a selectedcutting block and held in the selected cutting block with theinterconnection region 530 for various procedures. Also, the position ofthe cutting block 540 can be determined with the instrument 520 bypositioning the instrument 520 and using the navigation system 10.

Regardless, the instrument 520 may be efficiently connected with aninstrument or tool for determining a location of the tool. A user neednot hold or continually hold a probe relative to a tool when theinstrument 520 may be interconnected with the instrument for a selectedperiod of time. Therefore, the cutting block 540 need not permanentlyinclude a separate or its own tracking sensor, but may use the trackingsensor 522 interconnected with the instrument 520 for locating andtracking purposes.

Further, as discussed above, the instrument 520 may include the angledshaft 544 or straight shaft 526. It will be further understood that aplurality of shafts, including various angles, lengths variousconfigurations or geometries, or the like, may be provided. Each of theplurality of shafts, including a selected feature, may be interconnectedwith a single handle portion 524, which may include the tracking sensor522. Therefore, an inventory or kit may be maintained of the pluralityof the shafts 526, 544 without providing a plurality of the trackingsensors 522. Further, various or all portions of the instrument 520 maybe reusable or disposable. For example the shaft 526 may besubstantially disposable and the handle 524 may be reusable and or canbe sterilized. It will be understood, that this is merely exemplary andany portions maybe disposable or reusable. Moreover, the sensor 522 maybe wired or be wireless, such as that described above.

Although the instrument 522, which may include the tracking sensor 522,may be provided to be interconnected with the tool 540, it will beunderstood that the tool 540 may also include integrated trackingsensors. Therefore, although the instrument 520 may be interconnectedwith the tool 540 to assist in planning or tracking the position of thetool 540 relative to a selected portion, such as the tibia 550, thetracking sensor 522 may not be provided in the instrument 520, but maybe included in the tool 540.

Including the tracking sensor 522, or any appropriate tracking sensor inthe tool 540, may assist in minimizing the size of the tool 540 or theportion required to track the tool 540. Therefore, a position,orientation, or the like of the guide surface 544 of the tool 540 may bedetermined relative to the anatomy, such as the tibia 550. This mayallow for tracking a tool or a position of the tool 540 relative to theanatomy for a selected procedure. Further, the tool 540, if it includesthe tracking sensor, or is used with the instrument 520, may be used toachieve a planned procedure. Therefore, it will be understood that thetool 540 or any appropriate tool may include integral tracking sensorsrather than providing the instrument 520 separate or interconnectablewith the tool 540.

With reference to FIG. 27A, a DRF or a low profile DRF assembly 560 isillustrated. The DRF 560 may include a case or assembly housing 562 thatsurrounds one or more DRF sensors or coils 564 a, 564 b, 564 c, forvarious purposes, such as those described herein. As discussed above,the DRF 560 may be any appropriate DRF, such as an acoustic DRF, anelectromagnetic DRF, or an optical DRF. Nevertheless, as discussedabove, the DRF sensors 564 may include electromagnetic coils or coilsthat may sense a position in electromagnetic field, such that a directline of sight between the DRF sensor 564 and a receiver or localizer isnot necessary. Therefore, the housing 562 may include a size that allowsit to be positioned within a selected portion of the anatomy, asdiscussed herein.

For example, the DRF housing 562 may include a height that is less thanabout two centimeter or a height that is less than about one centimeter.It will be understood that the height of the DRF case 562 may be anyappropriate height to allow it to be positioned relative to a selectedportion of the anatomy. The case 562 may also include a shape orgeometry that allows a substantially smooth movement relative to softtissue of an anatomy, such as when the DRF 560 is positionedsubdermally. Thus the size and geometry of the case 562 may provide fora subcutaneous placement and movement of the DRF 560. The shape allowingfor the subcutaneous placement may be substantially short, such as lessthan about 2 cm. Also the shape may be substantially smooth to allow thesoft tissue to move over a surface of the DRF 560. This allows the DRF560 to be positioned and allow soft tissue to move relative to the DRF560 without the DRF 560 substantially interfering with the movement ofthe soft tissue.

The DRF 560 may be positioned relative to a portion of the anatomy, suchas a soft tissue portion or bone portion with a connection mechanism,which may include a screw 566 or a plurality of screws 566. In addition,as discussed above, the DRF 560 may include anti-rotation or fixationportions 568. The anti-rotation or anti-movement portions 568 may extendfrom a surface, such as a bottom surface 562 a of the DRF case 562. Theanti-rotation portions 568 may engage any appropriate portion, such as abony surface, a soft tissue portion, or the like to assist in holdingthe DRF 560 or the DRF sensors 564 in a selected location.

In addition, the DRF sensor 560 may be provided, such that it may bemoved relative to the soft tissue and then held in a selected position.Therefore, the DRF case 562 may include substantially soft or smoothsides that do not include sharp edges, such as would be found in asquare or other angular geometry. Nevertheless, it will be understood,that the DRF case 562 may be provided in any appropriate shape or size.

With reference to FIG. 27B, a low profile DRF 560′ is illustrated. Thelow profile DRF 560 may be similar to the low profile DRF 560illustrated in FIG. 27A. The low profile DRF 560′, however, may includeonly a single or a plurality of the screws 566 or a single or pluralityof the spikes 568. The spike 568 may act as an anti-rotation device suchthat the low profile DRF 560′ does not move or rotation relative to anaxis thereof. It will be understood that the low profile DRF 560′ or anyDRF according to various embodiments, generally may include at least twopoints of contact with a selected anatomical portion to substantiallyreduce or resist rotation of the DRF. Therefore, the low profile DRF560′ or a DRF according to any appropriate embodiment may beinterconnected with a portion of the anatomy for assisting in obtainingand maintaining registration of image space to patient space and the DRFmay maintain the registration by reducing or eliminating error due torotation. Therefore, the DRFs according to various embodiments, such asthe low profile DRF 560′, may include a mechanism to create two pointsof contact with the selected portion of the anatomy rather than aplurality more than two contacts.

The DRF 560, according to various embodiments, may be provided withvarious types of screws 566. For example, the screws 566 may besubstantially self tapping, drill tapping or any appropriate type ofscrew Therefore, the screw 566 may be positioned in a portion of theanatomy, such as bone, in a preformed hole or a hole that is tapped bythe screw 566.

Further, the screw 566 may be inserted in any appropriate manner. Forexample, the screw 566 may be captured in or held relative to any driverto assist in driving the screw 566 relative to the DRF 560. The screwmay be captured relative to the driver using a tapered fit or other typeof interference fit between the screw and the driver. Therefore, thescrew may be held relative to the driver, such that a generally onehanded driving may occur. The driver may be interconnected with a powerdrill or may be hand driven for inserting the screw relative to theanatomy through the DRF 560. Further, the screws 566 may be captured inthe DRF 560, such as in the body 562. For example, the bores or holes,through which the screws 566 pass, may include a locking or capturingtab to allow the screw 566 to be held relative to the DRF for a selectedperiod of time.

Further, it will be understood that the screws 566 may include anyappropriate driving form. The driving head of the screw 566 may beinclude a cruciform driving mechanism, a box, or square drivingmechanism, a hex driving mechanism, or any appropriate type ofmechanism. Further, the driving head may assist in holding or aligningthe screw relative to the driver to assist in positioning the screwrelative to the DRF 560.

Further, the DRF 560 or DRF according to any appropriate embodiment, mayinclude a body 562 that is substantially deformable or conformable. Forexample, the body 562 may include a substantially flexible body ormaterial that allows the body 562 to conform to the surface onto whichit is placed. For example, such as the DRF described above in FIG. 3,the DRF may include a portion that is flexible that engages the anatomy.Therefore, the DRF may substantially conform to the anatomical structureto assist in holding the DRF in a selected position. The body 562 may bedeformed with exterior pressure or when positioning the screws 566, orany appropriate holding mechanism, relative to the anatomy.

Although the body 562 may be flexible to assist in positioning the DRF560 relative to the anatomy. The tracking sensors 564A-564C of the DRF560 may be tracked by the tracking system in any appropriate manner. Forexample, the tracking sensors 564A-564C may be positioned within asubstantially rigid portion of the body with the body 562 beingdeformable relative to the rigid portion holding the tracking sensors564A-564C. In this way, the tracking sensors 564A-564C are held fixedrelative to one another to maintain registration of the DRF 560 relativeto a portion of the anatomy. Alternatively, or in addition thereto, thebody 562 may be substantially completely flexible such that the trackingsensors 564A-564C of the DRF 560 are able to move relative one toanother during the deformation of confirmation of the body 562. In thiscase, registration is performed after the DRF 560 is securely fixed tothe patient in its conformed condition.

Regardless, the DRF 560, or a DRF according to any appropriateembodiment, may include a body or structure that is able to conform to aselected portion of the anatomy. The deformation or confirmation of thebody 562 or any appropriate body may assist in holding the DRF relativeto the selected portion of the anatomy during a selected period of time.For example, although the DRF may be provided with a substantiallyplanar bottom 562A, it may be positioned relative to a non-planarsurface and deformation of the body 562 to conform to the non-planarsurface may assist in positioning or holding the DRF 560 relative to theselected portion of the anatomy.

According to various embodiments DRFs, such as the DRF 560 may be usedto position relative to soft tissue. As discussed above and herein a DRFmay be positioned relative to or in soft tissue and not obstructmovement of the soft tissue or other anatomical portions. With referenceto FIGS. 28A-28C an exemplary method is illustrated.

With initial reference to FIG. 28A an exemplary incision 574 may be madethrough a selected portion of soft tissue, such as dermis, skin, fascia,muscle, or any appropriate portion. The incision 574 may be used forperforming a selected procedure, such as those discussed above andherein. Nevertheless, it may be selected to position the DRF 560 at alocation M not at the location of the procedure. Thus the incision 574may be moved in direction of arrow N towards the selected location M.

Once at the selected location M, illustrated in FIG. 28B, the DRF 560,or any appropriate DRF, may be positioned. The DRF 560 may be fixed tobone, soft tissue, or any appropriate portion. Once the DRF 560 ispositioned at the selected location M the incision 574 may be moved backto its initial position, near where the procedure is to be performed,FIG. 28C. As discussed above this may allow a transdermal or sub-dermalplacement of the low-profile DRF 560, or any appropriate DRF. The DRF560 may be provided with a selected size or shape, such as a low profile(such as less than or equal to about 2 cm in height), to allow formovement of the incision after placing the DRF 560.

Thus the single incision 574 may be used to both position the DRF 560and perform a selected procedure. This may reduce incisions to be formedand decrease recovery time for the patient 14. Thus, the incision 574may be formed at a first location, the DRF 560 positioned, through theincision 574, at a second location, and the incision returned to a thirdlocation, which may be the first location. The sub-dermal placement mayassist in performing minimally or less invasive procedures, such asminimally invasive orthopedic procedures.

According to various embodiments, with additional reference to FIG. 28D,a portion of an anatomy, such as a leg 572 may exemplary have aprocedure performed relative thereto. For example, an incision 574 in asoft tissue 576, such as skin or muscle surrounding a selected portion,such as a femur 578, may be provided. The DRF 560 may be positionedrelative to a portion of the anatomy, such as the femur 578. The DRF 560including a selected size, such as less than about one centimeter inheight, may be positioned or fixed relative to the femur 578.

After positioning the DRF 560 relative to the femur, the incision 574may be unretracted or placed over the DRF 560. For example, a retractor580 may be used to move a portion of the soft tissue or expand theincision 574 for positioning of the DRF 560 on a particular portion ofthe femur 578. After positioning the DRF 560 relative to the femur 578,the retractor 580 may be removed and the soft tissue allowed to bereplaced or moved back over the DRF 560.

Once the soft tissue is positioned over the DRF 560, various tracking orlocalization procedures may be used to determine a position of the DRF560 and further determine a position of the femur 578 relative to otherportions. For example, a second DRF 582 may be positioned relative to atibia 584. Therefore, the DRF 560 may be used to determine a location ofthe femur 578 relative to the second DRF 582 and the tibia 584. Thesize, shape, orientation, and other features of the DRF 560 may allowthe DRF 560 to move relative to the soft tissue 576 surrounding the DRF560, after the soft tissue is replaced, and the femur 578. This may beuseful in determining a range of motion of the femur 578 relative to thetibia 584. It will be understood that a range of motion of any two bonesrelative to a joint may be determined using the DRF 560 and any otherappropriate DRF portions, such as the second DRF 582 or a second of theDRFs 560.

A range of motion may be determined after resurfacing a bone surface orpositioning an implant relative to a bone. The range of motion mayassist in determining a proper placement of a prosthesis or anappropriate resection or resurfacing of a bony portion. Therefore,allowing the DRF 560 to move with a bone portion, such as the femur 578,with the soft tissue in a substantially natural position, may assist indetermining a proper conclusion of a procedure.

Further, it will be understood that the DRF 560 need not be fixeddirectly to a bony portion. For example, the DRF 560 may beinterconnected with a selected portion of soft tissue, such as a muscle,a tendon, a ligament, or any other appropriate soft tissue portion. TheDRF fixed to a selected soft tissue portion may move with the softtissue portion relative to other portions of the anatomy or otherinstruments. Regardless, movement of the soft tissue may be determinedby use of sensing the location of the DRF 560, as discussed above.

Again, the DRF 560 may be provided in an appropriate size, geometry,location and the like to allow it to move relative to soft portions ofthe anatomy. The features of the DRF 560 may allow it to not obstructthe movement of the soft tissue to which the DRF 560 is attached or thesoft tissue relative to which the DRF 560 is moving. Thus, the DRF 560may be positioned and used to determine a movement of a bony portion, asoft tissue portion, and the like, where the DRF is moving and touchingthe soft tissue portions without interrupting the movement of thevarious selected portions. It will be understood that the DRF 560 may beany appropriate size, or any appropriate DRF. The DRF 560, or anyappropriate DRF, according to various embodiments, may include selectedsizes, shapes, and/or configurations to assist in movement relative tovarious selected locations. For example, the percutaneous orsubcutaneous placement of the DRF may be performed without requiring anexternal positioning or fixation of the DRF. Further, the DRF 560 may besubstantially wired or wireless to allow for various configurations andpurposes.

With reference to FIGS. 29 and 30, a mobile localizer 600, according tovarious embodiments, is illustrated. The handheld or mobile localizer600 may be similar to the transmitter coil array 46 and may be part ofthe electromagnetic navigation or tracking system 44. The mobilelocalizer 600 may be used in conjunction with or in addition to the coilarray 46. The coil array 46 maybe used to form a field until anobstruction is positioned that distorts the field and then the mobilelocalizer 600 may be used. Alternatively, both may be used together toassist in determining a location of the tracking sensor.

It will, nevertheless, be understood that the mobile localizer 600 maybe an instrument separate from the tracking system 44, but may includeportions or control systems similar to the tracking system 44. Thehandheld localizer 600 may include portions similar to the transmittercoil array that allows for localization, registration, and the like ofvarious portions, such as the DRF 54, any appropriate DRFs, such asthose discussed above, the probe or pointing device 66, or anyappropriate member.

The mobile localizer 600 may include any appropriate shape, size,geometry, and the like according to various purposes. For example, themobile localizer may include a first lobe or portion 602, a second lobe604, and the third lobe 606. Each of the lobes 602, 604, 606 may houseor define a transmitter coil positioned or included in the mobilelocalizer 600. It will be understood that the mobile localizer 600 mayinclude a substantially round, square, rectangle, or any appropriateshape. The lobe shape is merely exemplary and not limiting.

Further, the mobile localizer 600 may include a power and/ortransmission cable 608 interconnected with a selected power sourceand/or tracking system. For example, the cable 608 may interconnect themobile localizer 600 with the coil array controller 48 for transmissionand/or reception of a tracking signal. The mobile localizer 600,therefore, may be used to communicate or be operated by the system 44 toassist in tracking or locating a selected sensor, such as the DRF 54. Itwill be understood, however, that the mobile localizer 600 may also beinternally power or powered with a power signal. The mobile localizermay also include a wireless transmitter or receiver. This may allow themobile localizer to be substantially wireless.

Further, a handle or graspable portion 610 may extend from a housing 612defining the selected instrument. The graspable portion 610 may be usedto orientate or move the mobile localizer 600 relative to a selectedportion, such as the patient 14. It will be understood, however, thatthe mobile localizer 600 need not include a graspable portion 610. Auser, such as a physician may grasp the mobile localizer 600 directly.Also the mobile localizer 600 may be substantially wireless.

The mobile localizer 600 may include the casing 612 that is easilyremovable from the various coils held within the lobes 602, 604, 606.The casing 612 may be substantially sealable relative to a selectedexternal environment, such that a casing 12 may be easily sterilized andreplaced over the coils. The case 612 may also be disposable anddiscarded after a use. Alternatively, or in addition to the casing 12, asterile bag 616 may be provided to selectively surround a portion of themobile localizer 600. Therefore, the mobile localizer 600 may be used ina sterile environment through a plurality of applications withoutcontaminating the sterile environment. It will be understood that anyappropriate sterilization technique or portions may be used to insure asterile environment for the mobile localizer 600.

The mobile localizer 600 may include any appropriate selecteddimensions. For example, the mobile localizer 600 may include externaldimensions of about 50 cm². It will be understood, however, that themobile localizer 600 may include any appropriate dimensions, such asless or more than about 50 cm². Regardless, the mobile localizer 600 maybe moved by the physician or user 614 to any appropriate locationrelative to the patient 14.

With reference to FIG. 30, the mobile localizer 600 may produce a fieldLF that can be selectively directed over a selected area, such as asurgical area SA. The field LF, as discussed herein may be tuned orshaped for various reasons using various components and coilorientations. Further size of the field may be selected depending upon asize of the mobile localizer 600 and may be any appropriate size. Alsothe coils included in the mobile localizer 600 may be of a selected sizeto assist in selecting a size or strength of the field LF. Thus themobile localizer 600 may include various dimensions, such as a selectedarea or face 601 or volume (such as a three dimensional size). The area601 may be an area through which the field LF is focused or directedwhile a volume may be a three dimensional size of the mobile localizer600. The mobile localizer 600 may also include a mass of less than about2 kg, and may even be smaller than about 1 kg.

The mobile localizer 600 may include coils of any selected size. Thecoils, however, may be larger, and may be similar in size to coils usedin the coil array 46. Nevertheless, the coils in the mobile localizer600 may be positioned in an area, such as the area of the face, that iswithin a circle having a diameter of no more than about 16 cm (about 6in) or any appropriate dimension that may allow ease of movement by auser. Thus the area of the face 601, which may be equivalent to the areaof the coils, may be about 200 cm² or less. The size of the mobilelocalizer 600 may, however, be selected based upon an ergonomicconsideration for ease of use by a user, such as a one handed use by auser. Thus, the area of the face 601 may be less than 200 cm². Themobile localizer 600 may also include a volume that is about 1200 cm³ orless.

Nevertheless, the mobile localizer 600 may be moved such that the fieldLF is not obstructed or interfered with by an object O. The mobilelocalizer 600 may be moved by a user in any appropriate direction, suchas arrows 600 a, 600 b. It will also be understood that the mobilelocalizer may be moved to a new location to ensure that no or littleobstructions interfere with the field LF. Also, even if the field LF isless than the surgical area SA, the mobile localizer may be moved toensure that the entire area SA is covered by the field LF at a time.Thus the small mobile localizer 600 and the field LF may be used tocover a large area without requiring a large static or acquiredlocalizer. Nevertheless, both may be used together or separate. Forexample, the coil array 46 may be used until the object O createsinterference, then the mobile localizer could be used. Thus the trackingsystem 44 may switch between the coil array 46 and the mobile localizer600 or the two may be used together.

Moving the field LF may increase the accuracy or assist in determiningthe position of the DRF 54 or a coil in a sensor. For example, althoughthe surgical area SA may be an area including one or more of the DRFsthe object O may affect the field LF more in a first position than asecond position. The mobile localizer 600 may be moved to assist inreducing the affects of the obstruction O. Further, as discussed herein,various techniques may be used to determine a least affected coil orsensor. The mobile localizer 600 may be moved to assist in decreasingthe interference and increase the number of accurate coils or sensors.

It will be understood that the mobile localizer may be held by a hand oron a moveable portion for use. For example, the mobile localizer 600 maybe clamped or held relative to the bed 56. Also the mobile localizer maybe held by a user not performing the procedure.

The mobile localizer 600 may be positioned relatively close to aselected portion of the patient 14 for determining a location of aportion, such as a DRF 54 or an instrument. For example, the DRF 54 maybe positioned relative to the patient 14, such as subcutaneously usingthe subcutaneous DRF 560. The mobile localizer 600 may be positioned ata small distance, such as less than about one meter from the patient 14,to localize the DRF 54. It will be understood, however, that the mobilelocalizer 600 may be positioned at any distance from the patient 14,such as less than about twenty centimeters or less than about fiftycentimeters. Regardless, the mobile localizer 600 may be positionedsubstantially near the patient 14 for various purposes.

For example, the mobile localizer 600 may be easily or efficiently movedrelative to the patient 14 to substantially reduce metal effects on thefield produced by the mobile localizer. As discussed above, the mobilelocalizer 600 may produce an electromagnetic field that is used by thesystem 44 to determine a location of the DRF 54 relative to the mobilelocalizer 600. Therefore, the navigation system 44 may be used todetermine the position of the DRF on the patient or a selected positionof the DRF 54 relative to a second DRF 54′.

Further, the mobile localizer 600 may be used to reduce interferencefrom various portions or materials that may be present near the patient14. For example, the operative bed 56, the imaging device 12, or otherportions in a selected theater, such as an operating theater, mayproduce interference that may otherwise need to be accounted for in thetracking system 44 to determine an accurate position of the DRF 54, orother trackable portion. Positioning the mobile localizer 600substantially near the DRFs 54, 54′, however, may be used tosubstantially remove various interferences that may otherwise need to beaccounted for. The removal of interferences may allow for simplifyingvarious portions of the tracking system 44 or eliminating variousalgorithms that would need to be used to account for the interferences.

The mobile localizer 600 may be used, as discussed above to determine alocation of a tracking sensor. The tracking system may determine aposition of the sensor, such as one included in a DRF or the instrument52, relative to the patient 14 in the image space. As the mobilelocalizer 600 is moved relative to the patient 14 and the varioustracking sensors, the position of each can be determined with referenceto the fixed DRF 54, or DRF 54′. The position of the DRFs 54, 54′ may beknown or registered to the image space so that they may also bedisplayed on the display 36.

Further, the mobile localizer 600 may also be fixed to the patient 14.The mobile localizer 600, as fixed to the patient, may then produce thefield LF relative to the patient 14 from the fixed point on the patient14. In this instance the position of the various tracking sensors may bedetermined to the fixed position of the mobile localizer 600 on thepatient. Thus, it will be understood, that the mobile localizer may beheld by a used or fixed directly to the patient 14.

In either instance, whether held by a user or fixed to the patient 14,the affect of various interferences may be reduced or eliminated. Thefiled LF may be formed at and directed closer to the surgical area SA orarea of interest with a lower instance of interfering objects O. Also,the mobile localizer 600 may be positioned and aimed or directed towardthe surgical area SA in a manner to eliminate obstructions O from thefiled LF.

In addition, the mobile localizer 600 may be easily used to performlocalization and verification purposes, such as various optimization orverification steps may occur. For example, the field strength producedby the mobile localizer 600 may be substantially tuned, depending uponthe position of the localizer 600 relative to the patient 14 or the DRFs54, 54′. The field strength, or other feature, may be tuned or changeddepending upon a selected local environment. The tuning may be use toincrease the efficiency of the mobile localizer 600 and increase itsaccuracy. Regardless, the field strength need not be tuned for themobile localizer 600 and it may be used to perform the localizationaccording to various methods.

Further, the mobile localizer 600 may be integrated into any appropriateinstrument. For example, the mobile localizer may be integrated intovarious instruments, such as the probe 66 or the stylet 52. The mobilelocalizer 600 may be integrated into the instruments to reduce thenumber of instruments or portions in a selected operating theater and/orfor simplifying the performance of selected procedures. Therefore, themobile localizer 600 may be moved with the various instruments to assurethat the localizer is positioned near the DRF or the selected trackingsensor for determining a position of the tracking sensor. Also, asdiscussed above, the mobile localizer 600 may be incorporated into aninstrument fixed relative to the patient 14, thus possibly eliminatingthe DRF.

For example, the mobile localizer 600 may be integrated into the probe66, such that the field generated relative to the probe 66 may besubstantially tuned to provide a precise location of the probe 66 forthe navigation system 44. As discussed above, the field strength may besubstantially tuned for various applications to achieve selectedresults. In addition, providing the mobile localizer 600 near to aselected sensor, as discussed above, may substantially reduce metalinterference and improve metal immunity.

Therefore, it will be understood, that the mobile localizer 600 may beused to increase efficacy of the tracking system 44 according to variousembodiments. Although the mobile localizer 600 may not be required invarious applications, the mobile localizer 600 may be used to improvemetal immunity and reduce interference that may otherwise need to beaccounted for. Further, the mobile localizer may be positioned invarious orientations relative to the patient 14 or the localizersensors, such as the DRFs 54, 54′ for achieving a more precise signal.

Various systems, algorithms, and the like may be provided to furtherassist in increasing accuracy and efficacy of the navigation system 44.For example, a plurality of coils, such as greater than about two coilsfor an electromagnetic system, may be positioned in a sensor, such as aDRF. For example, any appropriate number of coils may be positioned in aDRF to be localized with the coil array 46 or the mobile localizer 600.The various coils may be used to provide an accurate determined positionof the sensor, according to various embodiments. For example, variousaveraging methods, weighting methods, or selection methods may be usedto determine a most precise sensed or determined location.

Various methods, according to various embodiments, may be used todetermine a location of a sensor, such as the DRFs 54, the probe 44, theinstrument 52, or any other appropriate portion. As discussed above, thevarious elements may include electromagnetic portions or coils thatallow for sensing and determining a location of the sensor. Thedetermined position of the sensor can assist in determining orinterpreting a location of a portion attached to the sensor, such as theinstrument, a portion of the patient, and the like. For example, each ofthe electromagnetic sensors may include one or more of conductors orinductive coils in which a magnetic field may be induced or sensed. Asone generally skilled in the art will understand, a magnetic field maybe produced with various elements, or a field or current may be inducedin the sensor. Therefore, it will be understood that any appropriateportion may be used to form an electromagnetic field or induce anelectromagnetic field in the sensor for various purposes.

Further, one skilled in the art will understand that a magnetic fieldproduced or induced in a selected portion may include both adeterminable position and orientation. Therefore, these sensed ordetermined positions and orientations may be used to determine aposition of a sensor, such as the DRF 54. Nevertheless, for variousreasons, a plurality of sensors or coils may be positioned in a sensor,such as the DRF 54. For example, various redundancies and increasedaccuracy may be achieved by providing a plurality of coils or sets ofcoils within the DRF 54, or any appropriate portion, for determining alocation and orientation of the DRF 54. It will be understood that thediscussion herein, though directed to the DRF 54, may be used in anyappropriate sensor for various portions, such as the instrument 52, theprobe 44, or any other portion. The DRF in the discussion of thefollowing methods and apparatuses is merely exemplary.

With reference to FIG. 31, a selected algorithm or method of averagingsignals 620 is illustrated. The averaging method 620 may generally allowfor averaging a plurality of sensed positions or points, such as aposition and orientation of a magnetic field, for determining a locationof the DRF 54. Generally, the averaging method 620 may make use of aplurality of sensed locations and averaging methods to provide a preciseposition of the sensor including the plurality of coils.

The averaging method 620 generally starts at start block 622. In thestart block 622, the DRF 54 may be positioned on the patient 14 (withreference to FIG. 1) or any other appropriate location. It will also beunderstood that various other steps may occur, such as registering theposition of the DRF 54 relative to the patient 14 and image space, if sorequired. It will be further understood that the navigation system 10may include the monitor 34 that may provide an image 36 of image spaceof the patient 14 and the position of the DRF 54 relative to the imagespace may be used. As discussed above, the DRF 54 may be used to insurethat the patient space is registered and matched to the image space forperforming a selected procedure.

After the procedure is initiated or started in block 622, magnetic fieldinformation may be received from the coils in block 624. It will beunderstood that the magnetic information collected from the variouscoils may include the position and orientation of the magnetic fieldsproduced or induced in the coils or any other appropriate information.Further, it will be understood that the DRF 54 may include anyappropriate number of coils, such as one, two, three, four or anyappropriate number. Further, any appropriate number of sets of coils maybe provided. For example, two sets of two coils may be provided in theDRF 54 at a known or selected geometry for various purposes, such asthose discussed herein. Nevertheless, each of the coils may be allowedto produce magnetic field information that may be collected in block624. Also, more than one of the DRFs 54 may be used together, such asdiscussed above. The localizer or tracking array may be used with anyappropriate number of the DRFs.

Briefly, as discussed above the sensor or DRF 90 may include the firstcoil 96 and the second coil 98 (FIG. 6). As illustrated the coils 96, 98may be placed in a selected geometry, such as an angle, relative to oneanother, such as an orthogonal angle. Although both coils 96, 98 may beformed about a single axis or origin. It will be understood that anyappropriate number of coils may be formed in the DRF 90, or anyappropriate DRF. Thus three or more coils may also be formed generallyorthogonal to one another about the single axis.

In addition to the DRF, such as the DRF 90, including more than onecoil, the DRF could include a plurality of sets of coils. With referenceto FIG. 27 the DRF 560 may include the first coil sensor set 564 a, thesecond coil sensor set 564 b, and the third coil sensor set 564 c.Though any appropriate number of sensor coil sets may be provided, threeare exemplary illustrated. The coil sets 564 a, 564 b, 564 c may bearranged in the DRF 560 in a selected geometry, such as shape,orientation, separating distance and the like. The geometry of the coilsets 564 a, 564 b, 564 c, may be known and used in various techniques todetermine the position of the DRF 560. It will be understood that anyappropriate sensor, DRF, or member may include the coil sets, coils, andthe like to assist in determining a position of the member.

The magnetic field information collected in block 624 of the coilsand/or sets of coils may be transferred to the work station 48 or anyappropriate processor, such as a microprocessor. As discussed above, theinformation may be transferred through various wired portions or may betransferred substantially wirelessly. Therefore, it will be understoodthat the DRF 54 using the method 620 may be a substantially wireless orwired instrument.

The positions of the coils may be computed in block 626 according tovarious methods, such as those described above or described in U.S. Pat.No. 5,913,820, entitled “Position Location System,” issued Jun. 22, 1999and U.S. Pat. No. 5,592,939, entitled “Method and System for Navigatinga Catheter Probe,” issued Jan. 14, 1997, each of which are herebyincorporated by reference. It will be understood that any appropriatemethods may be used to compute the positions of the received coils orthe magnetic field information received from the coils. Further, asdiscussed above, the position of various portions, such as the patient14 in the image space or of the instrument 52 relative to the DRF 54 maybe also determined. Therefore, the computation of the position of thecoils in block 626 may be any appropriate computation and further mayinclude various other relational computations.

After the position of the coils is computed in block 626, an averagingor combination technique in block 628 may be used to average thecomputed position. In block 628, the various computed positions of thecoils from block 626 may be geometrically combined using variousmethods. For example, a Single Value Decomposition (SVD), as is known inthe art, may be used to average the various computed positions of thecoils in block 626. Further, it will be understood that other averagingmethods may be used to average the computed positions of the coils fromblock 626. For example, averaging the positions, using other known leastsquares fit computation or any other appropriate averaging method may beused. Regardless, the various or plurality of computed positions of thecoils from block 626 may be averaged or combined in block 628.

The combined or averaged positions in block 628 may be used to determinea final position of the DRF 54. The various positions computed in block626 may each be a coil positioned within the DRF 52. Therefore, each ofthe coils may provide a position of the DRF 54. Nevertheless, to assistin assuring accuracy or reduce the effects of interference, such asmetal, space, etc., the plurality of coils, for which positions aredetermined or computed in block 626, may be averaged in block 628 topossibly increase the accuracy of determining the position of the DRF54. In other words, only a number of the coils, generally less than allof the coils or coil sets would be affected by interference, or thesignals received by them. Thus averaging the interfered andnon-interfered coil signals reduces, to an acceptable level, oreliminates error that may be created by the interference.

Further, in block 628 the various degrees of freedom, such as a sixdegree of freedom (6 DOF) transform may be determined. Thus, thecombination of the various computed positions of block 628 may provideinformation regarding the position and orientation of the DRF 54 in asubstantially precise manner. As discussed above, averaging the positionof the plurality of coils in block 628 may provide for a plurality ofposition information for the DRF 54.

Finally, the navigated position may be displayed in block 630. Theposition of the DRF 54, the instrument 52, or any appropriate portionmay be displayed on the monitor 34. As discussed above, the image spacemay be registered to the patient space or a position of the instrumentmay be displayed on the image space relative to the patient 14.Therefore, the navigated position determined using the method 620 may bedisplayed in any appropriate manner. As discussed above, the display mayinclude the monitor 34, may be a heads up display for the physician 614,or any appropriate display.

With reference to FIG. 32, a selection method for determining a positionof the DRF 54 is illustrated. It will be understood that although theselection method 640 may be discussed in relation to the DRF 54 that theselection method 640 may be applied to any appropriate portion. Forexample, the selection method 640 may be applied to determining anddisplaying a position of the instrument 52, the probe 44, or anyappropriate portion. Therefore, the discussion herein related to the DRF54 is understood to not be limited to the DRF 54 alone.

The selection method 640 generally starts in block 642. As discussedabove, various procedures may occur prior to the start block 642. Forexample, registering the image space to the patient space may beperformed or positioning of the DRF 54 on the patient 14 may beperformed. Further, various images may be obtained preoperatively of thepatient 14 for use in the selection method 640. Regardless, theselection method may generally begin at block 642 and allow fordetermination of the position of the DRF 54.

Similar to the averaging method 620, information regarding the magneticfield may be collected in block 644. Further, the position of the eachof the coils may be computed in block 646. As discussed above, each ofthe DRFs 54 may include a plurality of coils, such as any appropriatenumber for use in the method 640. Each of the plurality of the coils mayinclude unique magnetic field information, such as orientation andposition. Further, a plurality of sets of the coils may be provided inthe DRF 54, such as those described above in relation to FIGS. 6 and 27.Each of the coils and/or each of the sets of coils may be positioned ata known or selected orientations or geometry relative to one another.The known respective or relative positions or geometry may be generallyfixed relative to each of the coils or sets of coils for use in theselection method 640.

Once the position of the each of the coils or sets of coils is computedin block 646, the six degrees of freedom transform may be computed inblock 648. It will be understood that the 6 DOF transform may becomputed for each of the coils or the coil combinations according tovarious generally known methods, such as those described above or inU.S. Pat. No. 5,913,820, entitled “Position Location System,” issuedJun. 22, 1999 and U.S. Pat. No. 5,592,939, entitled “Method and Systemfor Navigating a Catheter Probe,” issued Jan. 14, 1997, each of whichare hereby incorporated by reference. The 6 DOF transform may becomputed to determine the geometry or position of the coils or sets ofcoils relative to one another.

In block 650, the computed geometry of the coils in block 648 may becompared to a known geometry in block 650. As discussed above, the coilsor sets of coils may be positioned in the DRF 54 or any appropriateportion at generally known or specifically known geometry. The computedgeometry in block 648 may therefore be compared relative to the knowngeometry in block 650.

For example, three coil sets may be positioned in the DRF 54. Each ofthe coil sets may include or be computed to have a sensed geometry orposition in block 646 and 648. The computed positions of the three coilsets may then be compared to the known positions of the three coil setsin block 650. For example, if the first coil set is known to be at aknown position relative to the second and third coil set, while thesecond coil set is known to be at a selected and known position,relative to the first and third coil sets, and finally the third coilset is at a selected and known position relative to the first and secondknown coil sets, those known positions may be compared to the determinedor calculated positions in block 648. Therefore, each of the coil setsmay be compared to the known positions of the coil set to the other coilsets. This comparison may be used to determine which coil set is leastaffected by various interferences.

The coil sets or coils least affected by interferences may be used todetermine the position of the DRF 54. As is known various items mayinterfere with a magnetic field produced or induced in the coils.Nevertheless, a position of the coils may be sensed and a sensedgeometry may be compared to the known and/or saved geometry of thecoils. As discussed above, the coils are generally fixed relative to oneanother. Therefore, in block 654 the coil set that gives the closestmatch to the known geometry may be selected. The coil set that mostclosely matches the known geometry is most likely the coil set leastaffected by interferences. The coil set least affected by interferencesmay provide the most accurate position of the DRF 54 for determining alocation of the DRF 54 relative to the patient 14 and for determining aposition of the patient relative to the image space.

Once the coil set is selected that is closest to the known geometry, aposition of the DRF 54 or the instrument 52, or any appropriate portionmay be displayed on block 656. The position displayed on block 656 maybe the position of one or more of the coil sets. As discussed above, theplurality of coil sets included for the selection method 640 may be usedto select a single coil set to determine a position of the DRF 54.Therefore, only one or more of the coil sets may be used to determinethe position and display the navigated position in block 656.

It will be understood that the selection method 640 may be combined withthe averaging method 620 to determine or display a position of the DRF54. For example, a plurality of coil sets such as the three, may beincluded for the selection method 640. More than one coil set may beselected in block 654 as being close or equally close to the knowngeometry. Therefore, the averaging method 620 may be used to average thetwo or more selected coil sets to provide further refinement fordetermining a position of the DRF 54. Therefore, after block 654,selecting the coil sets closest to the known geometry, the method mayproceed to block 628 of the averaging method 620 or may proceed directlyto block 656. That is the selected coil sets may be geometricallycombined or averaged in block 628. After combining or averaging the coilset in block 628, the position of the DRF may then be displayed in block656. Therefore, it will be understood, that any method may be used incombination with any other method or methods to determine a position ofthe DRF 54.

With reference to FIG. 33, various methods may be used to determine aposition of the DRF 54. For example, a weighting method 660 may be usedto determine a position of the DRF 54. It will be understood, asdiscussed above, that a position of the DRF 54 is merely exemplary andnot limited. Therefore, the weighting method 660 may be used todetermine the position of the instrument 52, the probe 44, or anyappropriate portion, such as an implant, to the patient 14 fordisplaying the image space 36. Therefore, the discussion below relatedto the DRF 54 is intended to be exemplary and not limiting.

The weighting method 660 may generally begin at block 662. As discussedabove, the start block 662 may include any appropriate preparation orsteps, such as positioning the DRF 54, obtaining images of the patient14 or any appropriate steps. Merely starting at block 652 is exemplaryand it will be understood to include any appropriate portions.

Further, as discussed above, magnetic field information may be collectedfrom the various coils in block 664. The collection of magnetic fieldinformation may be collected from any appropriate number of coils, suchas two coils, three coils, or any appropriate number of coils. Further,various magnetic field information may be collected from the sets ofcoils, rather than individual coils.

Magnetic field information collected from the coils may also includeinformation other than position and orientation of the field. Forexample, as one will understand, various other information, such asphase angle, frequency response, and other information regarding thenavigation of the instrument or the DRF 54 or information collected fromthe sensors in the DRF 54 may be collected in block 660. These variouspieces of information may be collected when the field informationregarding the coils is collected or at any appropriate time.

The various data or information collected in block 664 may be used toweight the information collected in block 666. Weighting the informationin block 666 may be used to determine or assist in determining theintegrity of the information collected in block 664. Various portions ormaterials, such as metal immunity, and the like, as discussed above, mayaffect the information collected in block 664. The various materials mayalso affect the additional information. Thus the various additional datamay be used to determine a relative affect of the various portions onthe field information being collected in block 664.

The additional information that may be collected in block 664, besidesposition and orientation of the magnetic field, may be used to weightthe information collected in block 664 to assist in determining theposition of the various coils and the DRF 54. The weights may be appliedin block 668 to the various pieces of data or to the equations regardingdetermining or evaluating the positions of the coils or the DRF 54. Oncethe weights are applied in block 668, the 6 DOF or position andorientation of the coils or the DRF 54 may be computed in block 670. Forexample, coils or coil sets that appear or are being affected more byinterference may be weighted less than those that are less affected.Thus, all information may be used according to its known or determinedweight, which can increase the accuracy of the tracking system.

Various methods may be used to compute the position or geometry of thecoil or coil sets, such as those discussed above, or generally known inthe art. Various methods may be used to compute the position of thecoils where the DRF 54 using the weighted data to determine a positionin orientation of the DRF 54 relative to the patient 14 and fornavigation.

Once the position and orientation is computed in block 670 with theweighted data or equations, the navigated position may be displayed inblock 672. As discussed above, the navigated position may be displayedat any appropriate display for various applications.

Therefore, it will be understood that according to various embodiments,more than one coil may be used to determine a position of an instrument,such as the instrument 52, the DRF 54, an implant (such as thosediscussed above), the probe 56 or any appropriate portion. The positionsof the coils may be used to register the image space to the patientspace, real-time register the image space to the patient space, ordetermine a position of the instrument, relative to the patient 14.Regardless, the plurality of methods, or any appropriate method, may beused to collect data from a plurality of coils. As discussed above theplurality of coils may be positioned in a single portion, such as asingle DRF, a single instrument, or the like, to assist in preciselydetermining the position of the instrument, the DRF, or the like. Thus,any appropriate portion or method may be used to assist or determine aposition of the DRF.

According to various embodiments, including those discussed above,various methods may be used to determine a position or axis of a portionof the patient 14. Various anatomical landmarks or geometries, such asan axis of a femur, humerus, or the like may be determined. For example,a transepicondylar axis may be determined by determining or finding aposition of a first epicondyle, such as a medial epicondyle, and asecond epicondyle, such as a lateral epicondyle.

With reference to FIGS. 34A and 34B, a distal end of a femur 700 may beprovided as a portion of the patient 14. It will be understood that thefemur 700 is generally surrounded by a portion of soft tissue 702,including skin, fascia, muscle, and the like. It will be understood thatthe FIGS. 34A and 34B are diagrammatic for ease of the followingdiscussion and are not detailed for clarity. The distal end of the femur700 may include a plurality of landmarks, including a first epicondyle704, and a second epicondyle 706. It will be understood that theepicondyles 704, 706 may be any appropriate epicondyle of the femur 700.For example, the femur 700 may be a left or right femur and thus theepicondyle 704, 706 may be medial or lateral condyles, depending uponthe femur selected.

Regardless, the epicondyles 704, 706 may define a transepicondylar axis708. The transepicondylar axis 708 is generally an axis or a linebetween the epicondyles 704, 706 drawn across or through the femur 700.

The transepicondylar axis 708 may be used for any appropriate procedure,such as a total knee arthroplasty (TKA). The transepicondylar axis 708may be used for positioning an implant, forming a resection of a distalportion of the femur 700, or any appropriate reason. Nevertheless,determining the transepicondylar axis 708 may be performed using anultrasound probe 710 and generally associated ultrasound equipment.

The ultrasound probe 710 may produce a cloud of points or information,such as the area 712 relative to the epicondyle 706 or area 714 relativeto the epicondyle 704. As discussed herein, this mosaic method may beused to determine a selected point. The ultrasound may be anyappropriate ultrasound, such as a mode A or a mode B. Regardless, theultrasound probe 710 may be moved across the soft tissue 702 relative tothe femur 700 for determining the epicondyle 704, 706. Various systemsfor using ultra-sound systems for registration are disclosed in U.S.Pat. Nos. 6,106,464 and 5,398,875. It will be understood that theultrasound probe 710 may also include a tracking sensor, similar to theDRF sensor, to allow the tracking system to track the position of theultrasound probe relative to the patient for use in the tracking system44. The various images and displayed images of the position of theultrasound probe 710 may be displayed on the display 34.

As is understood by one skilled in the art, the ultrasound may produceultrasonic waves that may be used to determine a position of a selectedanatomical portion through the soft tissue 702. Therefore, theultrasound probe 710 may be used to determine various anatomical points,such as the epicondyle 704, 706 without invading or passing through thesoft tissue 702. In addition, the ultrasound probe 710 may be used todetermine various anatomical landmarks or points using a substantiallyminimally or less invasive procedure when exposing the entire or distalend of the femur 700 is not generally performed.

As discussed above, the area of information 712, 714 generally near theepicondyle 704, 706 may be used to determine or compute the position ofthe epicondyle 704, 706. For example, the most medial or lateral pointsin the information areas 712, 714 may be used to determine the positionof the epicondyles 704, 706. These points maybe determined to be “high”points in the areas 712,714 and may be determined to be the epicondyles704,706 of the femur 700. It will be understood that various methods maybe used to determine the positions of the epicondyle 704, 706 accordingto various embodiments.

The determined points of the epicondyle 704, 706 may be displayedrelative to a patient image, such as a pre-acquired or preoperative CTscan, MRI scan, x-ray, or the like. Therefore, the determined epicondyleaxis 708 may be displayed on a display or image space of the patient 14without piercing the soft tissue to expose the femur 700. This may allowfor intra-operative planning and determining of the procedure withoutproducing further incision in the patient 14.

Further, the ultrasound probe 710 may be used to determine various otheranatomical axes or points. For example, a posterior condylar axis,anterior cortex point, tibial tubercle, anterior-posterior femoral axis,and the like may be determined with the ultrasound probe 710 and variousnavigation displays. For example, the navigation system 10 may be usedwith the ultrasound probe 710 to assist in displaying on the display 34an image of the patient 14 and the determined transepicondylar axis 708.Therefore, the display 34 may display a non-invasively determinedanatomical axis for use by a user, such as a physician for planning orperforming a selected procedure.

With reference to FIG. 35, the patient 14 may include a bone, such afemur 800 relative to a tibia 802. The bones, such as the femur 800 andthe tibia 802, may be surrounded by various portions of soft tissue 804,including skin, muscle, etc. The bones, such as the femur 800 aregenerally substantially contiguous and integral but may become damageddue to disease, injury, or the like. For example, a fracture 806 mayform in the femur 800. The fracture 806 may be repaired or held togethersuch that the femur 800 may again act as an integral bone with thevarious portions. For example, an intramedullary (IM) rod 808 may beprovided through an intramedullary canal of the femur 800. The IM rod808 may span the fracture 806 such that two or more portions of thefemur 800, or any appropriate bone portion, may be held relative to oneanother for use. The IM rod 800 may be positioned to allow for healingof the fracture 806 or for permanently holding the portions of the femur800 relative to one another. It will be understood, that although thefollowing discussion relates generally to the IM rod 808 and its use ina femur 800, that any appropriate bone portion or implant may be used toachieve a similar result.

Regardless, the IM rod 808 may be positioned through the intramedullarycanal of the femur 800 to span the fracture 806. It may be desired,however, to further fix the IM rod 808 relative to the femur 800 toensure that the various portions on the other side of the fracture 806are held relative to each other. Therefore, a fixation screw or pin 810may be provided that is operable to pass through a portion of the femur800 and a portion of the IM rod 808, such as a bore 812 formed in the IMrod 808. It will be understood that a plurality of screws may be used tofix the IM rod 808 relative to the femur 800 in a plurality of positionsor a plurality of points. Regardless, the screw 810 is generallypositioned such that it is operable to pass transversely through thebore 812 and not another portion of the IM rod 808.

The IM rod 808 may further include one or more of a tracking sensor 816.The IM tracking sensor 816 may be used to track a position of the IM rod808 with the tracking system 10, according to various embodiments.Further, the tracking sensor 816 may be any appropriate tracking sensor,such as those described above. Nevertheless, the tracking sensor 816 mayinclude an electromagnetic tracking sensor, an acoustic tracking sensor,a radiation tracking sensor, an optical tracking sensor, or anyappropriate tracking sensor. The tracking sensor 816 may be trackedusing the array 46 or the mobile localizer 600 according to variousembodiments. This may allow for determining a position of the IM rod 808and a bore 812 in the IM rod 808. The IM rod 808 may be used in an imageor imageless system for tracking the position of the IM rod 808.Regardless, the position of the IM rod 808 is tracked relative to thescrew 810, or vice versa.

The screw 810 may also include a tracking sensor 820 that is operable tobe tracked with the tracking system similar to tracking the trackingsensor 816 in the IM rod 808. Therefore, the screw 810 may be trackedrelative to the bore 812 in the IM rod 808. The tracking system may thenbe used to determine whether the screw 810 is positioned or will beinserted on a selected path to allow it to intersect to the bore 812after insertion into the bone 800.

The bone 800 may also include a DRF thereon, which may be anyappropriate DRF, such as those described above. Therefore, the imagespace of the system may be registered relative to the patient space andthe DRF 54 is used to maintain the registration should movement of thefemur occur. Further, the IM tracking sensor 810 may be used to track aposition of the IM rod 808 and the bore 812 in the IM rod 808 relativeto the screw 810. This may allow the screw 810 to be passed along aselected path, such as a path 824, to ensure that the screw 810 engagesand will pass through the bore 812 in the IM rod 808. Thus, the trackingsensors 816, 820 may be used by the tracking system in lieu of otherinstrumentation to ensure proper alignment of the screw 810 relative tothe bore 812.

Further, it will be understood that any appropriate implant may bepositioned relative to the anatomy. For example, rather than providingthe IM rod 808, the implant may be a bone plate 830 implant that isoperable to span the fracture 806.

With continued reference to FIG. 35, the bone plate 830 may also beprovided, or as an alternative to the IM rod 808, to span the fracture806. The bone plate may also include a bore 832 through which the screw810 or any appropriate screw may pass. In addition, the bone plate 830may include a tracking sensor 834 such that a position of the bone plate830 may be tracked. Therefore, as with the IM rod 808, the screw 810 maybe tracked relative to the bone plate 830 such that the screw will passthrough the bore 832 to allow for fixation of the bone plate 830relative to the bone 800 with the screw 810.

The various tracking sensors 816, 820, 832 may be used to allow foralignment of the screw 810 relative to the selected portion through asubstantially small or minor incision 840. in this way the incision mayremain small, but the positioning of the incision and the screw 810relative to the portion through which the screw will pass may besubstantially precisely determined, planned, and tracked with thetracking system. Therefore, a substantially open procedure or onerequiring various other external mechanisms, such as alignment guidesgenerally known in the art, may be reduced by using the tracking system.The tracking system is operable to allow for precise alignment of thescrew 810 relative to the portion through which it must pass to allowfor proper positioning of the implant relative to the bone 800 may bemaintained.

Further, the various tracking sensors may be any appropriate trackingsensors. For example, the tracking sensor may be integrated into theimplant such as the IM rod 800, the screw 810 or the bone plate 830.However, the tracking sensor may also be rigidly attached with selectedportion, such as the implant or an instrument positioning or holding theimplant relative to the anatomy. Various connectable or engageabletracking sensors include those disclosed in U.S. Pat. No. 6,499,488issued Dec. 31, 2002 entitled “Surgical Sensors”, incorporated herein byreference. Therefore, it will be understood that the tracking sensor maybe any appropriate tracking sensor and may be either integrated into theimplant or instrument or selectively attachable thereto.

Further, the DRF 54 or any appropriate tracking sensor positionedrelative to the femur 800 or the tibia 802 may be used by the trackingsystem to determine motion of the bones relative to one another. Themotion or articulation of the bones, such as the femur 800 relative tothe tibia 802, may be used to determine an anatomical plan, a range ofmotion, a joint line, a distance between various bones, or any otherappropriate measurement. The tracking sensors may be tracked by thesystem to display motion of the various portions of the anatomy on adisplay or for determining measurements of the anatomy. For example,this may be used to determine a position of the implant, such as the IMrod 808 or the bone plate 830 relative to the bone or any appropriateimplant, such as an articulated implant or the like.

The various portions of the anatomy may be measured to ensure that anappropriate distance, pre- and post-operatively is achieved or any otherappropriate measurement. For example, when repairing the fracture 806, alength of the femur 800 may be selected. Various tracking sensors,including the DRF 54, may be used to assure that the selected length isachieved post-operatively or intra-operatively, or if further adjustmentis necessary. Various types of joint measurements are disclosed in U.S.Pat. No. 5,772,594 to Barrick, issued Jun. 30, 1998, incorporated hereinby reference. Regardless, the tracking sensors used may include thetracking sensors discussed above and may be used by the tracking systemto ensure or assist in planning or determining the achievement of aselected surgical plan.

Various instruments can be used to perform the various procedures, suchas positioning implants, performing resections, positioning implants,and the like. The various instruments can be tracked to display aposition of the instrument during the operative procedure. The trackingcan be done with tracking sensors that can be positioned near or at adistal or working end of the instrument, or at any appropriate positionon the instrument.

As discussed above, various instruments can be used during a surgicalprocedure. For example, an instrument 900 can be an awl, probe, tap(APT) instrument, as illustrated in FIG. 36, according to variousembodiments. The instrument 900 can include a general or universal toolportion 902 and an interchangeable portion 904. The interchangeableportion 904 can be any appropriate portion such as a screw tap, a probe,or an awl. It will be understood that the interchangeable portion 904can also be any other appropriate member, such as a screw, a nail, afixation pin or the like. The interchangeable member 904 can be anyappropriate member that is operable to interchange with the standardportion 902 in an operable manner. The interchangeable member 904 mayinclude a quick connect portion, a tool engagement portion, and a threadportion, or the like, to connect with the tool portion 902.

The tool portion 902 and the interchangeable portion 904 can be formedof any appropriate materials. As discussed herein, the instrument 900can be tracked using an electromagnetic tracking system or any otherappropriate tracking system. If an electromagnetic tracking system isused, it may be selected to form the instrument 900 of a non ferrousmaterial such that it is not likely to interfere with theelectromagnetic tracking system. Therefore, the instrument 900 can beformed of titanium, other non-magnetic alloys, non-magnetic syntheticmaterials, or any appropriate materials. It will be understood that thevarious instruments described herein that are used with theelectromagnetic tracking system may all be formed of non magneticmaterials or any other appropriate materials.

The instrument 900 can be used with the navigation system 10. Thenavigation system 10 can be an image or an imageless navigation system.That is, as discussed above, images can be acquired of the patient 14and displayed on the display 34. Further representations of variousinstruments, such as the instrument 900, can also be displayed on thedisplay 34. Alternatively, the navigation system 10 can be substantiallyimageless such that the instrument 900 is illustrated relative to aselected point.

The navigation system 10 can be any appropriate navigation system, suchas an electromagnetic navigation system as discussed above. Theinstrument 900, therefore, can include a tracking sensor 906. Thetracking sensor 906 can be positioned at any appropriate positionrelative to the instrument 900. The tracking sensor 906 can generally beinterconnected with a bobbin or interchangeable member 908. Theinterchangeable member 908 can include a tool engaging end 910 that caninclude a quick connect portion that can interconnect with a toolengaging shaft 912. The interconnecting portion 908 can further includea handle engaging end 914 that is operable to engage a handle 916. Theconnections can be any appropriate connections such as quickconnections, permanent connections, threaded connections, or the like.

The tracking sensor 906 can be positioned at any appropriate position,but can be interconnected with the interchangeable member 908 such thatthe tracking sensor 906 is present in the various handles 916 and shafts912 can be interconnected with the interconnecting member 908. Thetracking sensor 906 can be positioned at a distance 918 from an axis 920of the instrument 900. The distance 918 can be any appropriate distance.For example, the distance 918 can be selected for operation by a user tominimize interference of the tracking sensor 906 with use of theinstrument 900. Nevertheless, the distance 918 can be known andunchangeable so that the position of the tracking sensor 906 relative tothe other parts of the instrument 900 can be known for determining alocation of any portion of the instrument 900.

The tracking sensor 906 can be any appropriate sensor or transmitter,such as an electromagnetic sensor including those described above. Itwill be understood that the tracking sensor 906 can include a pluralityof coils, such as three coils, that can be positioned relative to oneanother in a substantially selected manner. Further, the tracking sensor906 can be any appropriate EM sensor, such as a Hall Effect sensor.Thus, the use of coils is not required, but is merely exemplary. Forexample, the three coils can be positioned substantially orthogonal toone another and in a substantially fixed orientation to allow for up tosix degrees of freedom of tracking. The various types of the trackingsensors can include those described above or any appropriate trackingsensor.

The tracking sensor 906 can be wired or hard wired to the trackingsystem that is interconnected with a connector 920 and a wire 922. Itwill be understood that the tracking sensor 906 can also be a wirelesssensor. The connecter 920 can be interconnected with the navigationprobe interface 50, the isolator circuit 55, or any combination thereof.It will be understood that the instrument 900 can be interconnected in amanner substantially similar to the probe 52 discussed above. Therefore,the tracking sensor 906 can be used to track the instrument 900 in anyappropriate manner. Further, the connector 920 can be any appropriateconnector for connection with the navigation system 10. The illustratedconnector 920 is merely exemplary of any appropriate connector.

As discussed above, the instrument 900, including the distance 918, theconnector portion 908, the shaft 912, and the interchangeable member 904can have positions and orientations substantially known relative to oneanother. Therefore, the position of the tracking sensor 906 can be knownsubstantially relative to any other portion that is interconnected orinteracting with the tracking sensor 906. Thus, the instrument 900 canbe tracked, including any portion, thereof by determining the positionof the tracking sensor 906 and calculating a position of any of theother portions of the instrument 900 relative to the tracking sensor906.

The instrument 900 can be used for any appropriate procedure. Forexample, the interchangeable member 904 can include an awl for creatinga pilot bore or divot at a location, such as in a spinal portion. A tapcan be interconnected as the interconnectable member 904 to form atapped bore for receipt of a selected screw member. All of these may beused for performing a spinal procedure, such as for fixing a spinalimplant relative to a spine or any other appropriate procedure.

With reference to FIGS. 37 and 38, an instrument 940 is illustrated thatcan be similar to the instrument 900. The instrument 940 can include agenerally fixed or handled portion 942 and an interchangeable portion944. The interchangeable portion 944 can be similar to theinterchangeable portion 904 of the instrument 900. The handle portion942 can be similar to the handle portion 902 of the instrument 900. Theinstrument 940, however, can selectively not include the interchangeableportion 908, but simply include the rod engaging or tool engagingportion 946 and an operable handle 948.

Defined through the instrument 940 is a cannula 950. The cannula 950 canextend through the handle 948, the shaft 946 and the interchangeableportion 944. The cannula 950 can be formed in any appropriate dimensionand for any selected instrument, such as those described herein. Thecannula 950 can be operable to interact with the stylet 150. The stylet150, including the tracking sensor 162, as described above according tovarious embodiments, can be positioned through or in the cannula 950defined by the instrument 940. The stylet 150 can include the portionsdescribed above and illustrated in FIGS. 10A and 10B. Generally,however, the stylet 150 can be positioned in the cannula 950. Asdiscussed above, the tracking sensor 162 defined by a portion of thestylet 150 can be used to track a portion of the instrument 940. Asdiscussed above, positioning the stylet 150 within the cannula 950, asillustrated in FIG. 38, can allow for tracking any appropriate portionof the instrument 940 by tracking a position of the tracking sensor 162defined by the stylet 150.

It will be understood that the tracking sensor 162 defined by the stylet150 can be positioned at any appropriate position within the instrument940. That is the tracking sensor 162 can be positioned substantiallynear the interconnectable member 944, within the interconnectable member944, or within the fixed portion 942. If the tracking sensor 162 ispositioned substantially near a distal end of the instrument 940, suchas in the interconnectable member 944 or near the interconnectablemember 944, the tracking sensor 162 can be tracked to determine asubstantially precise location of the interconnectable member 944 or thedistal end of the instrument 940.

The stylet 150 can be interconnected with the handle 948, the shaft 946,or any appropriate portion of the instrument 940. Nevertheless, thestylet 150 can be provided in any appropriate dimension such that it isnonbinding inside of the cannula 950. Therefore, the instrument 940 canmove, or at least portions thereof can move, relative to the stylet 150,in particular the tracking sensor 162. Therefore, as the interchangeablemember 944 is moved relative to a selected portion of the patient 14 itcan be deformed or deflected, but its position can be substantiallyknown due to the positioning of the tracking sensor 162 on the stylet150.

As discussed above, the interconnectable member 944 can be an awl.Therefore, as the awl is being used a tip of it may deform or deflect,but the position of the interconnectable portion 944 is substantiallyknown. Similarly, if the tracking sensor 162 is positioned substantiallynear the interchangeable member 944, the shaft portion 946, which can beany appropriate length and formed of any appropriate material, can alsochange its dimensions while the position of the interchangeable member944 is still known. For example, the shaft 946 can be formed of adeformable material that allows it to flex under a selected load.Although the shaft 946 can flex under a selected load, the positioningof the tracking sensor 162 near or in the interchangeable member 944 canallow for tracking the position of the interchangeable member 944 due tothe fact that the tracking sensor 162 formed on the stylet 150 is nearthe distal end of the instrument 940.

It will be understood that the tracking sensor, such as the trackingsensor 162, can be formed in any appropriate manner, for example, thetracking sensor 162 can be formed on the stylet 150 according to anyappropriate method such as those described above according to variousembodiments. Therefore, the stylet 150 can be formed of any appropriatematerials. Nevertheless, it will be understood, that the tracking sensor162 can be formed on the shaft 946 or on the interchangeable member 944,itself. Although the selection of the material for the various portionscan be chosen to allow for formation of the tracking sensor on theinstrument 940 itself rather than the stylet 150, it will be understoodthat the stylet 150 can be used interchangeability.

Further, the stylet 150 can be used with any non-unique instrument 940.That is the stylet 150 can be positioned in any cannulated instrument toallow for tracking of a selected portion of the cannulated instrument.Therefore, the tracking sensor 162 is substantially portable and can beused with any appropriate instrument, such as those already existing inthe operating theater. But the stylet 150 still allows for tracking aportion of any appropriate instrument at a working or distal endthereof.

The stylet 150 can be wired including the wire 152, such as thatillustrated in FIG. 10A. Alternatively, the stylet 150 may includesubstantially wireless sensors, thus as generally known in the artincluding those disclosed in U.S. Pat. No. 6,474,341 to Hunter et al.,issued Nov. 5, 2002, incorporated herein by reference. Therefore, itwill be understood that the tracking sensors 162 can be any appropriatetracking sensors. The stylet 150 can be interconnected with thenavigation probe interface 50, the isolator circuit 55, or anyappropriate portion of the navigation system 10. Therefore, the stylet150 can be used to track the position of the instrument 940 or aselected portion of the instrument 940 even though the instrument 940may become deformed during an operative procedure. In addition, theinstrument 940 can be formed of any appropriate materials, includingthose that are appropriate for the instrument 900. For example, it maybe selected to the instrument 940 of substantially non-magnetic ornon-ferrous materials which may include various metal alloys orsynthetic materials.

With reference to FIG. 39, a guide instrument 980 is illustrated. Theguide instrument 980 can include various portions such as an externaltube 982, a handle 984, and a connection or collar portion 986. Theexternal tube 982 can be substantially hollow and define a cannula andcan also include a working end 988. The working end can allow foroperation of any appropriate portion, such as a drill bit relative tothe working end 988. The working end 988 may be interconnected or formedas one-piece with the tube 982 or formed substantially as a singlemember therewith.

The collar 986 can further define a cannula bore that interconnects withthe cannula bore defined by the tube 982. Positionable within the tube982 can be a spring 990, a sleeve 992 that can include a tracking sensor994 or any appropriate number of the tracking sensors 994. Positionablewithin the sleeve 992 is a drill bit 996. The drill bit 996 can includean extended shaft 998 and a drill tip 1000. The drill tip 1000 can beany appropriate drill tip. Further, the drill bit 996 can include a stopcollar or stop member 1002 for interacting with an appropriate portionsuch as with a proximal end 1004 of the tube 992. The collar 1004, orany appropriate portion, can also allow for a fixed connection of thesleeve to the drill bit 996. It will be understood that the drill bits996 may also include a tool engaging portion, such as a proximal end ofthe drill bit 996. The tool engaging portion can engage any appropriatetool such as a hand crank drill, a power drill motor, or any otherappropriate member. Nevertheless, the drill bit 996 can be positionedwithin the sleeve 992 to be positioned within the tube 982.

As discussed above, a substantially hollow cannula such as the suctiontube 190 illustrated in FIG. 13 can include the tracking sensors 206,208. It will be understood that the tube 992 can be similar to the tubeportion of the suction tube 190 illustrated in FIGS. 13 and 14. Further,the tracking sensor 994 can be substantially similar to the trackingsensors 206, 208 described and illustrated above. Therefore, detaileddescription thereof is not necessary herein.

Nevertheless, the tube 992 can be positioned within the exterior tube982 to offer tracking by the tracking sensor 994 once the tube 992 ispositioned within the exterior tube 982. As discussed above, thetracking sensors, such as the tracking sensor 994 can be tracked withthe navigation system 10. The tracking senor 994 positioned on the tube992 is operable with the drill bit 996 and can allow for tracking of aselected portion of the drill bit 996, such as a portion substantiallynear the drill tip 1000. Therefore, it will be understood that thetracking sensor 994 can be positioned on any appropriate portion of thetube 992 where the tube 992 can be formed relative to the drill bit 996.

During an operative procedure, the spring 990 may be positioned in theexternal tube 992 which can be followed with the sleeve 992 and thedrill bit 996. The drill bit 996 can be positioned within the trackingsleeve 992 and the unit can be positioned within the outer tube 992. Itwill be understood, however, that the assembly can be interconnected inany appropriate manner.

During operation, the drill tip 1000 can be advanced towards or out ofthe working end 998. As the drill at 1000 is operated, the trackingsensor 994 is able to be used to determine a position of a portion ofthe sleeve 992 substantially near the drill tip 1000. The spring 990 canalso be used to assist in determining a positioning of the drill tip1000. The spring 990 compresses a selected distance during operation ofthe drill bit 996. The compression of the spring 990 can be used todetermine an exact location of the drill bit 1000 even if the trackingsensor 994 is not substantially on or adjacent the drill tip 1000.Therefore, the instrument 980 can be used to determine a substantiallyprecise location of the drill tip 1000 during an operative procedureeven if the drill bit 996 becomes deformed during an operativeprocedure.

Further, the sleeve 992 allows for free rotation of the drill bit 996during an operative procedure, while still allowing for the trackingsensor 994 to be positioned substantially near the drill tip 1000. Asdiscussed above, the tracking sensor 994 can be formed on the tube 992substantially similar to the tracking sensors 206, 208 formed on thetube and the suction tube 190.

The sleeve can be substantially wired or wireless. For example, aconnector 1006 can be interconnected with the tracking sensor 994 andfurther connected with a wire 1008 to be interconnected with the probeinterface 50 or the isolator circuit 55. The tube 998 may include arecess or slot 1010 that is operable to allow for reveal of the sensorconnection 1006. It will understood, however, that the tracking sensor994 can be substantially wireless, as is known in the art.

Further, it will be understood that various portions of the instrument980 can be formed of selected materials, including those discussedabove. The instrument 980 can be formed of substantially non-magneticmaterials, including non-magnetic alloys, synthetic materials, or thelike. Nevertheless, the instrument 980 can be formed of materials toallow for the tracking sensor 994 to operate effectively to allow fordetermination of the position of the tracking sensor 994 and position ofthe various portions of the instrument 980 relative thereto.

As discussed above, positioning the tracking sensor substantially nearthe working end, such as the drill tip 1000, can allow for a precisedetermination of a position of the drill tip 1000 even if the drill tip1000 moves or is deformed relative to the shaft 998 of the drill bit996. Therefore, during an operation, such as during a spinal procedure,a cranial or neurological procedure, or the like, the position of thedrill tip 1000 can be substantially precisely known due to its proximityto the tracking sensor 994.

It will be understood that the tracking sensors, such as the trackingsensor 994 on the instrument 980 or the tracking sensors 162 on thestylet 150 can be provided as a plurality for tracking verification. Forexample, if two or more of the tracking sensors are provided, then thespatial position, including distance and orientation, between the two ormany should be substantially constant due to the materials rigidlyrelative to the tracking sensors. Therefore, the tracked location of thetwo tracking sensors on the same instrument can be used to determineaccuracy of the tracked system.

Further, as discussed above, the navigation system 10 using the trackingsensors near a working end or a distal end of the instrument can allowfor reduced calibration of the system. For example, the position of thetracking sensor is known to be near the working end of the instrument.Therefore, a calibration of a length of the instrument is not necessarybetween the working end of the instrument and the tracking sensor. Bypositioning the tracking sensor substantially near the working end, thetracking sensor is able to very accurately determine that position ofthe working end of the instrument, such as a drill tip or an awl.

With reference to FIG. 41, a tracking sensor 1020 is illustrated. Thetracking sensor can be any appropriate tracking sensor and may exemplarybe used as a dynamic reference frame, such as the dynamic referenceframe 54. The tracking sensor 1020 can be used as a dynamic referenceframe and can include a fixation base 1022 for fixation to a selectedanatomical portion, such as a boney portion including a spinal process,a femur or any other appropriate boney portion. The fixation base caninclude a bone engaging screw portion 1024 and a fixation platform 1026.The fixation platform can include teeth or projecting members 1028. Theprojecting members 1028 can engage the bone to assist in reducingrotation of the base 1026 relative to the portion to which it is fixed.Therefore, rotation of the tracking sensor 1020 can be substantiallyreduced or eliminated to allow for greater degrees of freedom oftracking.

The tracking sensor 1020 further includes a tracking head 1030. Thetracking head 1030 can include the tracking sensor coils 1032. Thetracking sensor coils 1032 can be any appropriate coils such as the coil90 illustrated in FIG. 6, according to various embodiments.Nevertheless, as discussed above, the tracking head 1030 can use anyappropriate sensor, rather than only coils. It will be understood thatthe sensor may be any appropriate sensor, such as any appropriate EMsensor including Hall Effect sensors. Although the tracking coils 1032can be fitted inside of the cap 1030, such as through molding orcasting, the tracking coils 1032 can be fitted to the cap 1030 accordingto any appropriate manner.

The cap 1030 further includes a base engaging portion 1034. The baseengaging portion 1034 can engage a portion of the screw 1024 such as aproximal or cap engaging portion 1036. The interconnection between thecap 1030 and the cap engaging portion 1036 can be substantially firm andresist rotation of the cap, including the tracking coils 1032 relativeto the base 1022, and therefore, relative to the anatomy to which thebase 1022 is connected. The cap engaging portion 1036 can include aportion that binds or engages the base 1026 to drive the engagingmembers 1028 into a selected portion of the anatomy to assist inresisting rotation of the base 1026. Further, the base engaging portion1034 can be keyed relative to the cap engaging portion 1036 to resistrotation or ensure a selected orientation of the cap 1030 relative tothe base 1022. The keyed portion or the anti-rotation feature can be theengaging portion is substantially non-cylindrical and includes aselected geometry.

Further, the base portion 1022 can be used as a fiducial marker. Forexample, the base 1022 can be fixed to a selected portion of the anatomyof the patient 14 during an imaging process to produce image data. Theimages can include the image of the base 1022 and the base can bemaintained in place prior to and during an operative procedure.Therefore, the base 1022, such as the cap engaging portion 1036, caninclude a divot or a marking portion that can be used to calibrate theimage space to the patient space.

Although the tracking sensor 1022 can be any appropriate trackingsensor, such as that disclosed in U.S. Pat. No. 6,499,488 to Hunter etal. issued Dec. 31, 2002 or U.S. Pat. No. 6,381,485 to Hunter et al.issued Apr. 30, 2002, each of which is incorporated herein by reference,the tracking sensor 1020 can be any appropriate tracking sensor. Forexample, the tracking 1030 can be substantially a single use member andcan snap onto the base 1022. Further, the cap 1030 can be formed in anyappropriate shape for use in the operative procedure. Also, the sensorcoils 1032 can be substantially integrally formed to form as a singlepiece with the cap 1030, such as molding the coils 1032 within the cap1030. Further, the coils 1032 can be substantially wireless or wired.Therefore, it will understood that a wire may extend from the cap 1030to interconnect the coils 1032 with the probe sensor 50. Nevertheless,the cap 1030 can be formed in such a manner to allow it to be onlydestructively removal from the base 1022. Therefore, the cap 1030 can besubstantially a single use cap for various purposes, such as insuringsterility, insuring operability, and the like.

With reference to FIG. 42, a tracking sensor assembly 1050 isillustrated, according to various embodiments. The assembly 1050 caninclude a tracking sensor cap 1052 that can be similar to the cap 1030in the tracking sensor assembly 1020. The cap 1052 can include sensorcoils (not illustrated) or any other appropriate sensor, such as thosediscussed above, and can be wired with a wire 1054 or wireless,according to various embodiments. The assembly 1050 can include aconnection portion 1056 similar to the connection portion 370 describedabove. It can, briefly, include a first leg 1058 and a second leg 1060that can be moved relative to one another with the fixation screw 1062.

The connection member 1056 can further include a connection post 1064.The connection post 1064 can include a sensor engaging portion 1066 andan anti-rotation or keyed portion 1068. The sensor engaging portion 1066can engage a complimentary portion of the sensor body 1052. Theconnection can be a snap engagement such that no other tools arerequired to interconnect the body 1052 and the post 1064.

The anti-rotation portion 1068 can also fit or engage with acomplimentary portion of the body 1052. The anti-rotation portion canassist in reducing or eliminating rotation of the body 1052, and thusthe sensors, relative to the connecter 1056. This can assist inincreasing the degrees of freedom of tracking that is possible if thesensor and the second body 1052 are fixed relative to the connector1056. It will be understood, however, that the anti-rotation portion1068 can be any appropriate portion. For example, any appropriategeometry, such as a polygon or square, can be used to resist rotationwith connection to the body 1052.

With reference to FIG. 43 a tracking sensor assembly 1080 isillustrated. The assembly 1080 can include a sensor cap 1082 thatincludes tracking sensors that can be wired with the wire 1084 orwireless, such as those discussed above according to variousembodiments. The sensor cap 1082 can be connected to a connector 1086.The connector can include a threaded body 1088 that can be threaded intobone or any other appropriate portion. The connector 1086 can,therefore, connect the cap 1082 and the sensor (not illustrated)included therein to a selected portion.

The connector 1086 can further include a cap connector portion 1089 thatextends from the body. The cap connector 1089 can be similar to theconnector 1064 described above. The cap connector can include a capfixing portion 1090 that is able to engage and hold a complimentaryportion of the cap 1082, such as that discussed above according tovarious embodiments. This connection can be a snap connection such thatno additional tools are necessary for the connection to be made. Furtheran anti-rotation portion 1092 can be provided. The anti-rotation portion1092 can also engage a complimentary portion in the cap 1082. Asdiscussed above the anti-rotation portion 1092 can be the depression orany other appropriate mechanism or geometry.

Further, it will be understood that the various portions of the trackingsensors according to various embodiments can be formed of selectedmaterials, such as non-magnetic materials including various syntheticmaterials or non-magnetic alloys. Further the cap or body portions,which can also be referred to as sensor body portions according tovarious embodiments, can be formed in a manner such that they are singleuse sensors and are destroyed upon removal from the connecting portions.Moreover, as described above, the snap connections can ease the use ofthe devices and increase operative efficiency.

This can also allow for of interchangeability. The same sensor body canbe moved from instrument to instrument in a selected procedure or frombase to base. For example, a sensor body can first be used as a DRF in aselected location on the patient 14, such as on the spine, and thenmoved to a second location, such as on a femur. Also, the sensor bodycan be moved from a DRF location to an instrument or vice versa. Thiscan decrease cost, inventory, and the number of items in an operatingtheatre.

The teachings herein are merely exemplary in nature and, thus,variations that do not depart from the gist of the teachings areintended to be within the scope of the teachings. Such variations arenot to be regarded as a departure from the spirit and scope of theteachings.

1. A navigation system for determining the location of a member relativeto an anatomy, comprising: a tracking system; a sensor assemblyincluding: a sensor and a cap sensor body operable to be sensed by saidtracking system; and a connection portion to interconnect said capsensor body with the anatomy having: an anatomy engaging portion thatengages the anatomy at a first location; a body connection portion thatextends from the anatomy engaging portion; and a rotation resistingportion coupled to the anatomy engaging portion that engages the anatomyat a second location different from the first location to resist therotation of the connection portion relative to the anatomy.
 2. Thenavigation system of claim 1, wherein said sensor includes anelectromagnetic sensor, an optical sensor, an acoustic sensor, orcombinations thereof.
 3. The navigation system of claim 1, wherein saidsensor includes a conductive coil, an inductive coil, or combinationsthereof.
 4. The navigation system of claim 1, wherein said trackingsystem includes a coil array operable to induce a magnetic field that isreceived in said sensor.
 5. The navigation system of claim 1, whereinsaid connection portion includes a projection operable to penetrate adistance into the anatomy.
 6. The navigation system of claim 1, whereinsaid connection portion includes a first leg and a second leg extendingrelative to one another.
 7. The navigation system of claim 6, whereinsaid first leg is movable relative to said second leg to engage theanatomy.
 8. The navigation system of claim 6, wherein said first leg isgenerally immobile relative to said second leg and said first leg isoperable to engage a first point and said second leg is operable toengage a second point of the anatomy to substantially reduce rotation ofsaid sensor.
 9. The navigation system of claim 1, wherein saidconnection portion includes: a base plate including projectionsextending from a portion of the base plate; a screw operable tointerconnect the base plate and the anatomy.
 10. The navigation systemof claim 9, wherein said projections resist rotation of the base platerelative to the anatomy.
 11. The navigation system of claim 9, whereinsaid connection portion extends from said base plate.
 12. The navigationsystem of claim 1, wherein said connection portion includes a spike, adrivable member, teeth, ridges, or combinations thereof.
 13. Thenavigation system of claim 1, wherein said connection portion isoperable to selectively engage said cap sensor body.
 14. The navigationsystem of claim 1, wherein said connection portion snap fits with saidcap sensor body.
 15. The navigation system of claim 1, wherein saidconnection portion engages said cap such that said cap must bedestructively removed from said connection portion.
 16. The navigationsystem of claim 1, wherein said sensor is integrally molded with the capsensor body.
 17. The navigation system of claim 1, wherein the capsensor body includes a recess that receives the connection portion. 18.The navigation system of claim 17, wherein the cap sensor body is keyedagainst rotation relative to the connection portion.
 19. The navigationsystem of claim 1, wherein the anatomy engaging portion extends throughthe rotation resisting portion.
 20. A navigation system for determiningthe location of a member relative to an anatomy, comprising: aninstrument having a first end and a second end; a working end definednear said second end; a first tracking sensor positioned at said secondend near said working end; a second tracking sensor positioned at saidsecond end, said second tracking sensor spaced apart from said firsttracking sensor; a tracking system operable to track said first andsecond tracking sensors; wherein said instrument includes a hollow tubeand said first and second tracking sensors extend helically about anouter diameter of said hollow tube at said second end; and a displaythat displays an icon representative of the working end of theinstrument superimposed on an image of the anatomy.
 21. The navigationsystem of claim 20, wherein said hollow tube defines an elongatedpassage, and the tracking sensors comprise electromagnetic sensor coilsthat are wound concentrically about said elongated passage.
 22. Thenavigation system of claim 20, wherein the first and second trackingsensors are spaced apart at a predetermined distance, and wherein thetracking system is further operable to compare a signal received fromthe first tracking sensor to a signal received from the second trackingsensor.
 23. A navigation system for determining the location of a memberrelative to an anatomy, comprising: a non-trackable instrument having afirst end and a second end, the instrument defining a bore and having aworking end near said second end; a stylet including a plurality oftracking sensors formed helically around an axis of said stylet, saidstylet received within the bore such that the stylet extends from thefirst end to the second end of the instrument and such that saidtracking sensors are positioned near said second end; a tracking systemoperable to track said tracking sensor to thereby determine a locationof the working end of the instrument; and wherein said instrumentincludes a handle at the first end and an interchangeable member thatcomprises said second end, and each of said handle and saidinterchangeable member define a bore for receipt of at least a portionof said stylet.
 24. The navigation system of claim 23, wherein saidstylet is operable to be positioned in said instrument.
 25. Thenavigation system of claim 23, wherein said stylet is operable to befixed relative to said instrument.
 26. The navigation system of claim23, wherein the bore has a closed end.
 27. The navigation system ofclaim 23, wherein the bore has an open end.
 28. The navigation system ofclaim 23, wherein the stylet includes a handle that extends beyond anend of the handle of the instrument.
 29. The navigation system of claim28, wherein the handle of the stylet includes at least one electricalcontact that is in communication with the tracking sensor and incommunication with the tracking system to transmit a signal from thetracking sensor to the tracking system.
 30. The navigation system ofclaim 23, wherein the stylet is received within the instrument so thatthe tracking sensor is not exposed.
 31. The navigation system of claim23, wherein the stylet is interconnected to the instrument.
 32. Thenavigation system of claim 23, wherein the non-trackable instrumentengages the stylet to prevent the stylet from extending out of thesecond end of the non-trackable instrument.
 33. A method of tracking atracking sensor with a tracking system to determine the location of aworking end of an instrument, comprising: positioning a non-trackablecannulated instrument having a first end and a working end relative toan anatomy; slidably inserting a stylet having a plurality of trackingsensors helically wound around an axis of the stylet near a distal endinto the cannulated instrument such that the stylet extends from thefirst end to the working end of the cannulated instrument and such thatthe plurality of tracking sensors are near the working end of theinstrument; tracking the plurality of tracking sensors with the trackingsystem; determining a location of the plurality of tracking sensors; anddetermining a location of the working end of the instrument according tothe location of the plurality of tracking sensors.
 34. The method ofclaim 33, further comprising: deforming the instrument; and maintainingthe plurality of tracking sensors near the working end of theinstrument.
 35. The method of claim 33, wherein determining a locationof the working end of the instrument substantially includes determininga location of the plurality of tracking sensors.
 36. The method of claim33, further comprising: displaying an icon representative of thelocation of the working end of the instrument superimposed on an imageof an anatomy.
 37. The method of claim 33, wherein inserting the styletfurther comprises: inserting the stylet having the plurality of trackingsensors helically wound about the distal end of the stylet.
 38. Themethod of claim 33, further comprising: guiding the working end of theinstrument to a desired position within the anatomy; and performing aprocedure on the anatomy with the instrument.
 39. The method of claim33, further comprising interconnecting the stylet to the instrument. 40.The method of claim 33, wherein slidably inserting the stylet includespreventing the distal end of the stylet from extending out of theworking end of the cannulated instrument.